Interactive Troubleshooter

NOTE: Yes, this article is very long. However, on the 'PRODUCTS' catalog at we hope to feature newer and simpler mileage enhancers as they are released to the worldwide market. Cost may vary, but we expect significant reduction in installation and tuning time. If you don't find what you need there, Mike Kehrli usually has the best and latest enhancers at



CAUTION: Never run an engine with a lean mixture unless you have some kind of a water system (Electrolyzer or Vaporizer, such as .) installed and functional. The presence of HHO/water is vital to cool down the engine and to prevent pinging and knocking.

The article below has been edited from materials researched, experimented and documented by Mike Kehrli from and Mike Holler from

It is next to impossible to give you an exact road map for mileage tuning, like "if you have a Mercedes Benz 1980, model so-and-so, then this is exactly what you need to do". We're getting closer and closer to having such a road map. However, it will take years before we have a complete and simplified road map (data base of all vehicles WITH their specific solution). I wish I could give it to you right now on a silver platter but it seems that nobody knows everything about it.

So, for the time being, you should read this article completely at least twice before jumping into action. Because this knowledge might not work in parts, it has to be complete knowledge. Specifically, you must be aware of ALL the sensors to be dealt with, as well as ALL available methods and solutions that may or may not fit your vehicle.

Due to his ethics level (no "secrets" held back) and his high level of hands-on knowledge, I have chosen Mike Kehrli to be our expert on tuning the ECU. You can always contact Mike - AFTER READING THIS ARTICLE TWICE, PLEASE - by email

This article describes ALL computer enhancements (via the sensors, i.e., without touching the computer itself), and focuses on enhancing the OXYGEN SENSOR. For more information on enhancing other sensors, refer to the Water4Gas books and DVD's.


Not all modern fuel injection system are created the same, but a typical system may include the following sensors:

  • Oxygen Sensor (O2 Sensor)
  • Intake Air Temperature (IAT) Sensor
  • Mass Airflow (MAF) Sensor, also called "Intake Air Flow Sensor" or Air Flow Meter"
  • Exhaust Temperature Sensor (the "Oxygen Sensor" near the catalytic converter)
  • Manifold Absolute Pressure (MAP) Sensor
  • Throttle Position Sensor (TPS)
  • Fuel Pressure Sensor
  • Barometric Pressure Sensor
  • Engine Speed Sensor
  • Knock Sensor.

Sometimes it's hard to find what type and number of sensors your vehicle has. Between so many car models, a source of reliable information is necessary. Also, we want it to be easy to use. There are many ways to do this. Here's a suggestion for online users of this book: use

  1. To start searching, visit
  2. Choose your auto maker. You can do this by scrolling down, or by searching for a brand name in the search box. NOTE: I tried to type the entire description of my car, and found nothing. Then I found out that it must be in a specific format (Year, Make, Model, Engine); you can change the sequence (for example Make, Engine, Model, Year), but you must add commas and leave spaces after each comma. For example: toyota, 1999, 1.8, corolla.
  3. Select the manufacturing year, then model. You can do this either by clicking the small + sign next to the line, or clicking the line itself.
  4. A list of information groups will be displayed, by system type. Select "Emission".
  5. The list will now expand to show what type of emission-related sensors and parts are available in that specific vehicle. In the example shown below, I searched for the MAP Sensor types for my Toyota, 1999, Corolla, 1.8 liter.
  6. When you click on each of the small photos, a larger photo will be displayed. This can help you identify the sensor once you see it in the engine.



When dealing with the intricate jungle of ECUs, sensors and all of that, you must use proper factory information. For a low monthly subscription, these guys give you everything you need: DETAILED WIRING DIAGRAMS, Factory Diagnostic Flow Charts, Trouble Codes, Factory Repair Procedures, Diagrams & Part Numbers, Research Tools and much more. Try the following sources:

[Ozzie Freedom]


By Mike Holler and Mike Kehrli, with comments by Ozzie Freedom

The Need

So you installed one or several devices all claiming up to a 30% increase in mileage, but you are only seeing maybe a 10% gain. There are many devices and technologies on the market and the Internet that are based on sound science that can't seem to deliver the goods.

It has become painfully obvious by observing my apprentices on the mpgResearch Forum that a comprehensive Guide to Tuning is desperately needed. Simply making combustion more efficient these days isn't enough. The factory ECU is programmed for the factory hardware. Once you deviate from that basic recipe, the ECU is no longer able to deliver optimal results.

The Fix? Tuning!

Tuning a stock vehicle usually won't deliver much of an increase in mileage. Up to 20% gains have been reported, but typically fall into the 10% or less range. Once you add something to improve combustion efficiency, much larger gains are common. In fact, I've been seeing over 100 MPG regularly with Brown's Gas, fuel heaters, vaporizers, ozone, and other devices, almost always in combination.

Let's break the tuning process down into bite-sized steps. A logical format makes the tuning process more like science and less like a mystical black art.

  1. Verify the vehicle is in good working condition
  2. Install your mileage device(s)
  3. Lower your lean-out limits
  4. Adjust your air/fuel mixture
  5. Adjust your ignition timing
  6. Readjust your air/fuel mixture.

Step 1: Verify Vehicle Condition

A common cause of vehicles fighting mileage gains is a hidden problem with the vehicle itself. Tired oxygen sensors, clogged EGR (Exhaust Gas Recirculation*) circuits, carboned throttle bodies, ignition components that are not up to par, partially clogged catalytic converters, defective sensors, and a whole host of other problems have been found. Usually the vehicle runs perfectly fine, no codes are set, and the stock mileage is typical for that type of vehicle. The owner assumes that the vehicle is in top operating condition because he/she has no reason not to.

* For the differences between EGR, PCV and Catalytic Converter functions, visit
(~Ozzie Freedom)

When the proper tuning procedure is followed and mileage gains just won't come, go back and start nit-picking the vehicle apart. Check everything. You might even consider planning on a complete tune-up at this time. In fact, this would be a good time to upgrade to Pulstar Plugs, MPG Plus ignition wires, Blue Streak or Neihoff cap and rotor. Clean out your throttle body and PCV system. Install new filters and oxygen sensor. Make sure the basics are in order.

Step 2: Install Mileage Device

The next step is to install your mileage device or devices (such as Water4Gas Electrolyzer). Many people like to install upgrades one at a time to determine the overall effect each addition yields. Some like to just toss several on at a time. Usually finances dictate the one-at-a-time method. Be sure to install the device(s) properly. If it is a product you have purchased, follow the manufacturer's instructions to the letter. If it is a device you have built from plans, perhaps from the internet, again, follow the instructions implicitly.

Any other modifications called for in the instruction manual should also be done at this time. Some devices require other changes in order to be effective. Without the other changes, the inventor cannot guarantee the results you seek. Short cuts usually short-cut your results.

Step 3: Lower Lean-Out Limits


What NASA Says About Lean Mixtures

"Lean-mixture-ratio combustion in internal-combustion engines has the potential of producing low emissions and higher thermal efficiency for several reasons. First, excess oxygen in the charge further oxidizes unburned hydrocarbons and carbon monoxide. Second, excess oxygen lowers the peak combustion temperatures, which inhibits the formation of oxides of nitrogen. Third, the lower combustion temperatures increase the mixture specific heat ratio by decreasing the net dissociation losses. Fourth, as the specific heat ratio increases, the cycle thermal efficiency also increases, which gives the potential for better fuel economy."

"The results were used to explain the advantages of adding hydrogen to gasoline as a method of extending the lean operating range. The minimum-energy-consumption equivalence ratio was extended to leaner conditions by adding hydrogen, although the minimum energy consumption did not change. All emission levels decreased at the leaner conditions. Also, adding hydrogen significantly increased flame speed over all equivalence ratios."

NASA Technical Note D-8487, March 15, 1977
Lewis Research Center, National Aeronautics
and Space Administration, Cleveland, Ohio

~NASA side note added by Ozzie Freedom

The ECU has parameters that it will not go beyond. The parameters that are correct for your modified vehicle almost always fall outside the range the ECU is prepared to operate. Combustion efficiency enhancing technologies will easily take your maximized operating conditions beyond what the ECU will tolerate. The solution is to change the parameters.

The ECU works similarly to our brains. It uses multiple inputs and controls multiple outputs. We have our 5 senses: hearing, sight, smell, taste, and touch. Within each of these senses there are a range of different inputs possible. The ECU has its senses as well: MAP (Manifold Absolute Pressure), TPS (Throttle Position Sensor), MAF (Mass Air Flow), ECT (Engine Coolant Temperature), IAT (Intake Air Temperature), Tach, O2 (oxygen sensor) and other inputs.

If the MAP sensor sees a given load, the TPS sees a corresponding throttle angle, the CTS (Coolant Temperature Sensor) sees a normal operating temperature, and the O2 sensor is saying the engine is too rich, the ECU will comply…to a point. When the ECU has leaned out the AFR (Air/Fuel Ratio) beyond what the programming claims is an acceptable range, the ECU will go into Open Loop and ignore the O2 sensor. It then reverts to Look-Up tables for its source of information. At this point, mileage will invariably go down, and often a trouble code is set.

Consider the conditions needed for the ECU to accept lean fuel commands. If the engine is warmer than it actually is, the ECU will accept leaner. If the engine is under less of a load, the ECU will want to deliver less fuel. If the incoming air is hotter, the ECU will accept lean commands more readily. If MAF (Mass Air Flow) sensor equipped, less air entering the engine will require less fuel.

Now let's look at the particulars.


One of the easiest ways to lower lean-out limits is to install a resistor across the CTS and IAT sensors in parallel with the sensor. A parallel circuit offers 2 paths of travel for the voltage. A cold CTS will have very high internal resistance. As it warms up, the resistance goes down. Adding a parallel resistor nets a lower total resistance value, thus sending a hotter temperature signal to the ECU. It should be noted that this trick applied to the IAT sensor will retard ignition timing in addition to lowering the lean-out limits.


Most of the world uses similar resistance values to equate a given temperature. The Ford based systems (including Mazda, Infiniti, and Jaguar) use much higher resistance values. This is important to know when selecting resistors. If you have a scan tool available to you, use it. Monitor the CTS temperature that the ECU sees. With your engine at operating temperature, check to see that the temp reading is close to the thermostat rating. If it is, proceed. If it isn't, check your cooling system for contamination or stuck thermostat. You may need to do a coolant flush or repair before proceeding. Assuming you are getting reasonable numbers, try different resistors across the CTS to raise the temp reading about 10° F (for example, from 195° to 205°). Even though higher numbers will work, you will most likely run into cold start issues beyond the 10° offset. The average vehicle will use something like a 3.9K ohm resistor. Fords may like a 5K ohm or larger value. (a 7.5 K Ohm or 10 K Ohm "trimmer" or trim-pot may be useful to find the ideal point) (Ozzie F.)

If your cooling fan runs continuously with your setting, add more resistance to lower the temp reading. Any mileage gains from the hotter engine signal will be more than offset by the additional load on the alternator. If you have a rear-wheel-drive with a belt driven fan, you can still add too much temperature offset. The ECU has an internal cooling mode. After the engine overheats to a point, the ECU starts dumping copious (plentiful, rich) amounts of fuel. The excess fuel will evaporate, thus cooling the engine from the inside. However, at this point your mileage literally tanks.


The IAT is less sensitive to cold start issues. You can add more temp to this signal than you can to the CTS. Just keep in mind that you are not only lowering your lean-out limits, you are also retarding your ignition timing. If you put a timing light on the engine as you adjust IAT values, you won't see the timing change. The timing changes under load. Hotter air is more prone to detonation. This is why the ECU retards the timing.

If you are tuning on the hottest day of the year, you may find out just how high of a signal you can generate before setting codes. Typically it is in the 240° F range. If you are tuning in the middle of February, then you can offset the signal from your base cold reading and things will be fine for now. Come June or August, this setting may be high enough to trip codes. Allow for this when tuning.


Notes by Ozzie about MAP: I hear many readers say "MAP Sensor" when talking about the ENHANCER that tunes the MAP signal. The enhancer is not the sensor! The MAP Sensor is part of the car, while the enhancer is just that, an enhancer that we add to the car in order to fine-tuning the MAP signal. Also note that NOT ALL MODERN CARS HAVE MAP SENSORS.

The MAP sensor is located on the intake manifold itself, just before the engine block, or mounted separately on the back of the firewall and connected with a thin vacuum tubing to the engine block.

It is important to address your load sensing system in order to keep your mileage gains. Often times addressing only a few of the ECU's inputs will allow you to tune for a mileage gain, only to have the adaptive memory take it away as time goes on. The load sensing devices give the ECU a clue as to what you are up to, and it won't tolerate it. By generating a lower voltage signal from the MAP sensor, harmony is restored, and your mileage gains are for keeps.

There are 2 types of MAP sensors on the market. Most of the world uses a version that has a 5 volt VREF (reference voltage, or in other words the signal), ground, and DC signal wire. The MAP is a type of potentiometer; like a radio volume knob. Instead of turning the knob with your hand, the knob is turned as the vacuum in the engine changes. A high vacuum reading will give a low voltage signal. A low vacuum reading will give a high voltage signal. Low vacuum means the engine is under load and needs lots of fuel. Look at it this way, low signal voltage, low fuel requirements. High signal voltage, high fuel requirements.

If you raise the VREF, then the signal will be higher. If you lower the VREF, then the signal will be lower. A lower signal tells the ECU lower load. A relatively simple method of lowering the VREF is with an LM317T adjustable voltage regulator. If you are somewhat capable with electronics, you can build one for about $10 to $15. The parts you will need are:

  • LM317T adjustable voltage regulator
  • 220 ohm resistor (1/4 watt is sufficient)
  • 1K ohm multi-turn potentiometer (Trim pot)
  • Small heat sink for the LM317T
  • 3 different colors of 18 gauge wire
  • Enclosure (box).

Note by Ozzie: the diagram below, by Mike, displays an alternative design to the Water4Gas MAP Sensor Enhancer described in our books and DVD's.

The functional difference is that Mike's device (below) uses a voltage regulator, LM317T, feeding from 12 Volts, to supply a different SUPPLY voltage to the car's sensor. DEMSE, the Dual-Edge MAP Sensor Enhancer that I've developed (see DVD 3 or my books) simply takes the OUTPUT of the sensor - without changing its input - and attenuates (reduces) that output using a potentiometer.

Personally I prefer DEMSE because it gives me two KNOBS to play with at any given time. However, both designs will do the job of fine-tuning the MAP signal.


The LM317T comes in a TO-220 case. Looking at it from the front with the mounting tab at the top and the 3 pins at the bottom, solder the 220 ohm resistor across the 2 left pins. Run a jumper wire from the left pin to the center of your 1K pot. Run a ground wire to one of the outside legs of the pot. If you use one side, then clockwise will raise the voltage. If you use the other side, then counter-clockwise will raise the voltage. Bench test your unit to know which way it will work.

Run the right leg to a Key-On/Crank battery voltage source. It is important that you have voltage when the key is on AND when cranking. If you don't have voltage when cranking, the ECU will not see a MAP signal and usually won't start at all. Drill 2 holes in your enclosure; one for the wires and one to access the pot.

With your unit on the bench, apply battery voltage to the battery and ground leads. Check the voltage output. Adjust it to 5.0 volts to start with. To install it on your vehicle, cut the VREF wire going to the MAP. DO NOT TAP THE VREF WIRE COMING OUT OF THE ECU! This will affect all sensors using the same 5 volt signal and will deliver disastrous results. After you cut the wire, connect your adjusted voltage wire to the MAP sensor and tuck and tape the other end of the cut wire back into the harness. It is best to solder connections and seal with heat-shrink tubing.

Lowering the VREF voltage will lower your lean limits, but will also advance ignition timing. Less load equals more timing advance. More load equals less timing advance. Remember this when we get to step 5.

The other type of MAP sensor used almost exclusively on the Ford based systems is frequency based. It has a 5 volt VREF, ground, and frequency signal output. The method of dealing with the frequency based MAP sensors is different than that used for the DC voltage based MAPs. Simply cut the ground wire going to the sensor, then add a small amount of resistance. A good starting point is about 10 ohms. Your upper limits will be between 15 and 20 ohms, depending on the ECU's calibration. The more resistance, the more offset. Notice I didn't say 10K ohms. It takes very little resistance to accomplish the job. You may find an Ohm Ranger or small value potentiometer (more or less 30 ohm) helpful here. Note: Another tuner has found that his 90 Ford pickup needed higher voltages than described here - see his forum post.

User notes:
"I have tested different resistance levels on both the input and ground circuits of the MAP. I have determined that adding resistance to the ground of the MAP does work, but not at the levels in the article. I have found you need a much higher resistance to achieve the desired outcome. I am hesitant to state an exact resistance as all vehicles are different but you should expect to be somewhere between 100 ohms to around 1000 ohms or more. I tested this by using a hand held vacuum pump while monitoring the Hz and changes at different vacuum levels and changed the resistance at each level.
If you are looking into this mod I would highly recommend a multi turn pot for making adjustments. Multi turn will make it easier to fine tune. I have 10-turn 10k pots with counters and locks to make testing easier.
One main issue I found is that the frequency changes were not fully equal at all vacuum levels with the same resistance. For example the resistance that changed the frequency 1 Hz at 20"hg
[*see def. below] would change the freq at 0"hg by about 3-4 Hz."
-Written by 'excite'

*hg: inches of Mercury, the usual unit for measuring vacuum.


1Water4Gas Map Sensor Enhancer >>>

This very popular device is very simple and low cost. That's why it's so popular for tuning the MAP Sensor - if the vehicle has such a sensor. It consists of a plastic box, two variable resistors (potentiometers or "pots" for short), two regular resistors, a switch and a couple wires. If you have basic training in electronics and can solder parts together, you can build this device in one afternoon. A single-pot version would actually look like this:


And a dual-pot version would look like this:


The advantage of the dual pot version is only this: you can tune your mixture once for the highway, and once - separately - for the city or cold start conditions, then leave both pots where you have tuned them. Now all you do is switch from one position to the other. Refer to the Water4Gas Books and DVD's for complete instructions on building and tuning this device.



There are a couple different styles of MAF sensors that have been employed over the years. Early versions were called Vane Air Flow (VAF) sensors. They had a spring loaded door that controlled a wiper arm across a resistive pad. There is a black plastic cover that, once removed, will allow access to this resistive circuit. Raising spring pressure will lower lean-out limits. You can shift the wiper arm to a clean spot on the resistive circuit to extend the life of your VAF while you're in there.

Some of the MAF sensors work like the typical MAP sensors in that they have a DC voltage IN, and a DC voltage signal OUT. They can be dealt with the same as the typical MAP sensor.

Most of the modern MAF sensors have a ground, battery voltage input, and frequency based output. These aren't that difficult to tune. I've seen complicated and expensive products that aren't much better than this trick. Just like the frequency based MAP sensors, cut the ground wire and install a small amount of resistance. Again, no more than 30 ohms, with averages in the 10 to 15 ohm range.

User notes:
"The newer MAF sensors are 4 wire. If it's a 6 wire, 2 of the wires are for the IAT. As for altering the MAF, resistance in the tan wire with the blue tracer has worked well for me. The range I've used is in the 150k to 330k range. On '03 and newer Ford products, the resistance dropped down to the 25k to 50k range."


Step 4: Adjust the AFR

There are low cost devices that monitor the AFR, the Air/Flow Ratio:



Once you have set the stage by lowering your lean-out limits, you can now adjust the AFR for better mileage. The exact method will depend on the type of O2 sensor your vehicle uses. There are 4 types currently on the market: old style oxygen sensor, AFR sensor, titania sensor, and wide-band sensor. Each requires its own unique approach. Some vehicles may have 2 bank sensors. You'll have to address both equally. Don't worry about the downstream sensors (the ones after the cat) as they only tell the ECU that the converter is working.

To do your adjustment, you want to monitor your Loop Status. If your ECU pops into Open Loop, any adjustments you make are irrelevant. You have to stay in Closed Loop. If you pop into Open Loop, your lean-out limits are still too high (or your oxygen sensor is bad). If you can install a scan tool to monitor Loop Status, do it. This is the easy way. If you have an older vehicle that doesn't have data stream information, then hook a digital volt meter to the O2 signal wire. As long as the voltage is jumping around, you're probably in Closed Loop. If the voltage goes steady, you probably are in Open Loop.

As you begin to lean out the mixture you will probably feel an increase in power. There will be a peak in the power, then it will gradually taper off. After so much leaning out, it will be like you just fell off a cliff. There will be a dramatic loss in power, it will want to hesitate and stall. I try to tune about ½ way between peak and cliff.

Old Style O2 Sensor

The oxygen sensor was introduced in mass back in 1981 on GM vehicles. It has an operating range of 0-1 volt. The higher the voltage, the richer the detected AFR. The lower the voltage, the leaner the AFR. A rich mixture is a lean command. A lean mixture is a rich command. It is commonly called a Narrow-Band sensor because it is only accurate within a narrow range of AFR operation. Right at the 14.7:1 AFR, a small change in AFR yields a large change in voltage. As the engine goes leaner or richer from the 14.7:1, the voltage changes get smaller and smaller.

A device that has been used for several years is the Electronic Fuel Injection Enhancer (EFIE) developed by George Wiseman of Eagle Research. The principle is to create a small amount of voltage offset that is electrically isolated from chassis ground. It is like a free-floating battery installed inline with the signal wire. This raises the voltage to the ECU indicating a richer-than-actual AFR.

If you have an older vehicle with loose parameters, you may be able to add as much as 0.450 volts to the O2 signal. If you have a newer vehicle with tight parameters, you may not be able to get away with more than about 0.280 volts. Experimentation will dictate what your ECU will tolerate.

The old single wire sensors are easy to spot the signal wire, since it is the only one. There have been 2-, 3-, and 4-wire sensors used over the years. You may have to use a manual to determine which wire is the signal wire. Usually on a 4-wire sensor, you have 2 white wires for the heating element, a gray wire that is ground, and a black wire for your signal out.

Another method that I have not personally tried, but comes with good recommendations is to drill out a spark plug anti-fouler for the mid-70s Ford products with the 18 mm plug. Install the modified anti-fouler into the exhaust where the O2 sensor normally goes, then screw the O2 sensor into the anti-fouler. This pulls the sensor out of the exhaust stream and allows for leaning out the AFR. Since I haven't tried it, I cannot guarantee results.

Wide Band Sensors

Good news! You can use the same EFIE on the signal wire of a wide band. The one wide band that I modified used the blue wire for the signal. Wide bands will have 5 wires. That's the dead give-away. They have been used widely on VWs and Mazdas.

AFR Sensors


AFR sensors operate under a totally different set of rules. The same sensor is used in 2 different ways by various OEMs (Original Equipment Manufacturers). One method involves putting a fixed voltage on the reference wire (white) and varying the current to maintain a fixed voltage on the signal wire (blue). Another method is to apply a fixed voltage and current to the reference wire, and monitor the voltage coming out. Either way, they are current devices, not voltage devices.

To alter an AFR sensor, cut the blue signal wire and install low value resistors. The range will be 30 ohms or less. Most of the vehicles I've modified have liked the 7 to 18 ohm range. I've never needed over 20 ohms as of yet. Again, an Ohm Ranger or low value pot will be helpful in your tuning. You will be able to feel 1 ohm resistance change.

Note from Mike Kehrli,

"We have not had luck using a resistor on an AFR sensor. If you do this handling, please document your mileage before and after this one step, and if you have success, please contact me and let me know. We recommend doing the MAP and temp sensor handlings if you have AFR sensors.

Titania Sensors

They work similarly to the traditional O2 sensors, but backwards. I haven't yet had the opportunity to deal with these, so I can only give you guesses on what will work. One possibility is to install an EFIE backwards so you are lowering the signal voltage. Another way might be to add resistance to the signal wire. The spark plug anti-fouler may also work. Fortunately, they were only used for about 3 years and only on select vehicles (mainly European such as Vauxhall, as well as a few Asian models such as Subaru).

Step 5: Adjust Ignition Timing

If you have a distributor, the solution is simple. Loosen the hold-down clamp and turn the distributor. If you have DIS (Distributorless Ignition System), COP (Coil On Plug), or a distributor that doesn't affect timing, then you have to play with the MAP and IAT signals to dial in the spark.

To adjust with the distributor, grab a vacuum gauge, timing light, and distributor wrench. Drive the vehicle down a relatively flat section of road at cruise speed. Watch your vacuum gauge. Pull over and either advance or retard the timing by about 4 degrees. If you increased the power and vacuum, adjust again by about 2 degrees. If you lost power and vacuum, crank it the other way about 8 degrees and test again. You want the least amount of timing advance needed to maintain maximum power at cruise. Any more advance than that will increase the possibility of detonation, and will fight the piston on the compression stroke.

If you have the DIS or COP, adjust the IAT sensor reading by 10° F increments for maximum power. If you start high on your reading (smaller value resistor), start adding resistance to advance timing. If you have a near ambient reading (no or large value resistor), reduce parallel resistance to retard timing.

As stated earlier, adjusting the MAP VREF will alter timing. A lower VREF will advance timing. A higher VREF will retard timing. There is a balance between finding the right lean-out limit, and maximizing the timing.

Step 6: Readjust AFR

Improving combustion efficiency usually requires less timing advance to get the job done. The fuel burns faster and more thorough. Thus, it takes less time to convert the chemical energy in the fuel into kinetic energy at the crank. On the flip side, as you lean out the AFR, it takes longer to burn across the leaner mixture. More timing advance is required. Sort of a catch-22. Once you have adjusted your ignition timing for maximum power, you may find that you can lean out your AFR a bit more. A leaner mixture requires more time for the flame to propagate across the cylinder. If you advanced your timing, try leaning out the AFR a bit more. If you retarded your timing, you might be able to slightly enrich the AFR and get better power and mileage.

Tuning was taught in tech schools up until about 30 years ago. As the vehicles became more complex, there was less tuning required for optimal performance and mileage. Tech school grads coming into the work force these days are taught to follow flow charts, replace bad parts, and track down poor connections. For the younger generation, tuning is something they read about in magazines, but never get to experience. It isn't difficult, but requires a learning curve just like anything else. Don't get discouraged quickly. It may take a little time to get the hang of it, but you can do it.


Oxygen Sensor Adjustment - General Information

Almost all modern vehicles employ oxygen sensors to tell the vehicle's computer if the air/fuel mixture is too rich or too lean. The computer uses the information from the O2 sensor to determine if more or less fuel should be added to the mix in order to maintain the correct proportion.

Gas vehicle engines (as opposed to diesel engines) are designed to operate at an air/fuel ratio of 14.7 to 1. When these proportions are being supplied to the engine, a certain amount of oxygen will be detected in the exhaust by the O2 sensor, and this information is fed into the vehicle's computer. If more oxygen is sensed, the computer thinks the mixture is too lean (not enough fuel), and adds fuel to the mix. Likewise, if less oxygen is sensed, the computer thinks the mixture is too rich (too much fuel) and cuts back on the fuel fed to the engine.

There's a big problem with this scenario as soon as you start adding a workable fuel efficiency device. For any given air/fuel ratio, burned more efficiently, the oxygen content in the exhaust will rise. If you have two or more efficiency devices installed, even more oxygen will be present in the exhaust. The oxygen content rises as the fuel is burned more efficiently for a number of reasons. Chief amongst these are:

a) less fuel is being used to produce an equivalent amount of horsepower, and

b) less oxygen is being consumed to create carbon monoxide in the exhaust. The bottom line is there is more oxygen in the exhaust as the fuel burning efficiency is increased.

So, now that we have spent time and money to install a fuel efficiency device or two, and we are getting a more efficient fuel burn, what does the vehicle's computer do? It dumps gas into the mix in an attempt to get an oxygen reading in the exhaust equal to its earlier, inefficient setup. This will then negate the fuel savings of just about any efficiency device, and in some cases will actually cause an increase in fuel consumption, despite having a workable fuel efficiency device.

The Solution

The handling for this situation is simple. The signal coming from the O2 sensor needs to be adjusted to compensate for the increased fuel efficiency being achieved. Basically the added oxygen in the exhaust fools the computer into thinking the mixture is too lean, causing it to (incorrectly) richen the mix. We need to un-fool the computer so it continues to give us the same amount of gas as before. We do this by making it think there is less oxygen in the exhaust than there actually is. The amount of change to the signal has to be easily adjustable to accommodate the different types of efficiency devices that are available.

The oxygen sensor produces voltages to communicate the oxygen content to the computer. When the sensor reads below .45 volts, that means it's lean, and when it reads above .45 volts, it's saying the mix is rich. If you connect your volt meter to an oxygen sensor signal wire and ground, while the engine is running, you'll see the voltage is constantly changing, and you'll probably see voltages in the range of .3 to .7 volts or so. In actual fact, the voltage is changing back and forth from about .1 volt to about 1.0 volts, several times per second. But a hand held meter is not quick enough to show this.

The EFIE adds it's voltage to the sensor's voltage, which shifts the voltage that the computer receives towards rich. This causes the computer to provide less gas. Many people think we're trying to fool the computer with an EFIE. That's actually not accurate. The extra oxygen in the exhaust because of a more complete combustion is what's fooling the computer. It's making the computer think the mix is too lean, and it's compensating by adding gas that is not needed. The EFIE is un-fooling the computer. All we want to do is get it back to giving us a 14.7 to 1 air/fuel ratio again.

It should be noted that an oxygen sensor handling device, by itself, is not a fuel efficiency device. It possibly could be used to control the vehicle's computer, and make the engine burn a little leaner, and this could possibly give a small increase in gas mileage. But this is not what it was designed to do. It was designed to complement, and in some cases make possible, increased gas mileage using other fuel efficiency devices.

If you need to purchase an EFIE for your project, you can find them at FuelSaver-MPG specializes in accessories for fuel saving devices such as the EFIE and have a number of different models to suit different applications and budgets.


Using ScanGauge for Fine Tuning?

You can't use a ScanGauge when tuning an EFIE. The ScanGauge uses the oxygen sensor's data, which is being modified. As the ECU (and ScanGauge) think the AFR is 14:7 to 1 with the EFIE on and off. But with the EFIE on, it's actually leaner. The only way to test is by actual road tests. Once you get everything working the way you want, then you calibrate your ScanGauge to read correct MPG with your setup.

While tuning you should just read the ScanGauge to help you with your MAP sensor tuning, and also for your temp sensors if you tune them. The ScanGauge can tell you what temp it's seeing.

Between the MAP enhancer and the EFIE you'll have an effective control over the ECU and air fuel mix. You might want to do the temp sensor modifications as the final step. With all of these done, the ECU will not be able to relapse, because all of the sensors it uses to compare to the oxygen sensor are also modified, giving you stable gains.

After all is done, and you've maximized your mileage, then calibrate the ScanGauge to give you correct mileage readings (how to do that – see the ScanGauge manual).


EFIE: Electronic Fuel Injection Enhancer, Described

As you can see from the title, EFIE stands for Electronic Fuel Injection Enhancer. It was developed for fuel injected vehicles, and was found to be necessary in order for other fuel efficiency devices to work on them. This includes virtually all cars and trucks today.

Photos of EFIE Devices

(clicking any of these photos takes you to Mike's store)

Single EFIE


Another thing that is fundamental about an EFIE, is that it is not a fuel efficiency device on its own. If all you did was add an EFIE to your car, with no other fuel efficiency system, you might gain a few mpg, but you also might not. The reason is that you are fooling the car's computer and making it run out of spec, or differently than it was designed for. The EFIE was designed to make the car run according to spec after another fuel efficiency device has been installed.

The purpose of the EFIE is not to provide fuel efficiency. It's purpose is to make it possible for other fuel efficiency devices to work. Basically a fuel efficiency device makes the engine think something is wrong, and makes it do things to adjust for this "wrongness". The actions it takes based on the oxygen sensor data, makes it negate the efficiency increase that would have been realized by the efficiency device. The EFIE solves this by adjusting the signal to the computer so the computer is happy with the readings it's getting and it's making the correct adjustments for the various conditions of the engine. Basically, the oxygen sensor tells the computer it's oxygen readings by providing a voltage between 0 and 1 volt. In order to adjust this "data" the EFIE adds a small voltage to that delivered by the oxygen sensor. The EFIE is highly adjustable. Adjustments to the trim screw can change the EFIE's voltage correction by tiny amounts; a millivolt or 2 (0.001 volt).

The EFIE works on a delay. When the engine is started, the oxygen sensors are cold and do not send correct data to the computer. We don't want to modify this data until the sensor is operating correctly. The EFIE will build up to its rated voltage offset over 3 to 5 minutes, longer in very cold weather. Also, when you turn the vehicle off, the EFIE loses its voltage offset slowly. This means it will more quickly jump back into full operation if the car is re-started again after a short stop. This is by design, but you need to know about it when trying to adjust your EFIE. When you make a change, you'll see your meter start changing, and keep changing after you've stopped turning the adjustment screw. The bulk of the change will occur after the first minute, but if you have a sensitive meter, you will see it minutely increase for up to 10 minutes.

In practice, with a good fuel efficiency system installed, you might want to have the EFIE adjust the signal from about 250 - 400 millivolts. Complete installation instructions are given below.

If you would like to purchase a pre-built EFIE, you can find it at, as well as a Dual EFIE unit, designed to handle 2 oxygen sensors here. Both of these units have been designed to be economical, easy to install, and easy to adjust to your particular car and fuel saver combination. And they come with full money back guarantees.


What Do I Need To Know About My Oxygen Sensor?

How Many EFIEs Do I Need?

This question comes up a lot. There are literally thousands of models of car, and each has its own design. The number of oxygen sensors can vary from one to four or more. Do all of them need EFIEs to operate properly with fuel saving devices?

The short answer is, that all oxygen sensors on the engine side of the catalytic converter need EFIE devices. It is rare that there are more than 2 of these. Eight cylinder engines tend to have 2 sensors, one on each exhaust manifold, but often have only one. Six and four cylinder engines tend to have 1 sensor, but can have more. Regardless, all of these upstream sensors must be treated.

The sensors after the catalytic converter, or attached to it, are there to tell the engine computer when the catalytic converter has gone bad, but are not used to modify the calculations on how much gas to give to the engine. The upstream sensors are the ones telling the computer what it needs to know about the combustion mix.

What Type Of Sensor Do I Have?

This is an important question to answer. There are a number of different types of sensor, and some are handled differently. Oxygen sensors for many years were of a single type. These were more specifically called narrow band oxygen sensors, and EFIEs are designed to work with these. In recent years, a new type of sensor has come out, the wide band oxygen sensor and EFIEs are not designed to work with some of them.

The most easily identifiable form of wide band sensor is the one that has 5 wires. The 5-wire wide band sensors reportedly work with an EFIE. If you use an EFIE on one of these sensors, I would appreciate an email telling me how it works for you, the settings you used, etc, because I don't have any personal experience with these. But I'm told by reliable sources that they have used EFIEs successfully on 5-wire wide band sensors.

There is another variety of wide band sensor that uses 4 wires, that you must be aware of. These are not actually called oxygen sensors (although that's what they are). They are called Air Fuel Ratio (AFR) sensors. EFIEs are definitely known to NOT work with these sensors.

How do you know if you have an AFR sensor or narrow band oxygen sensor? You might get lucky and have it written on the vehicle information tag on your hood. Open the hood and look up. It may be written there. Otherwise, you will need some documentation for your vehicle. I don't mean the owner's guide that is given to you when you buy your new car. If you're going to be installing modifications to your engine, you should have a Haynes, Clymer or Chilton's manual for your car or truck, preferably Haynes as these are generally more informative. If you have an AFR sensor, it will be called such in the diagram. Otherwise it will be called, "Oxygen Sensor" or "Heated Oxygen Sensor" or sometimes HEGO (Heated Exhaust Gas Oxygen) sensor. Lastly, I have found a new resource where you possibly can get all of this information for free at AutoZone's web site (look under "Repair Info" and after selecting your model and year, select "Wiring Diagrams" in the repair guide).

If you read the EFIE Installation Instructions below, you'll see there's another reason to have a good wiring diagram for your car. That is so you can find the wires for your sensor(s) up near the computer, where you can easily access them. Believe me, they are worth the money for that alone. But if you have any doubt about the type of sensor you have, they are doubly valuable.

If all else fails in determining what type of sensor(s) you have, use the EFIE Installation Instructions and read through section "1. Locate the oxygen sensor signal wire". This will describe how to determine which wires have which function from your oxygen sensor. If you have a narrow band sensor, you will find a signal wire that behaves as described in the instructions. If you have an AFR sensor, you will get different electrical phenomena entirely.

What Color is My Oxygen Sensor Wire?

The following link has a table that will help you identify the correct signal wire. First, identify the MAKE of the Oxygen Sensor itself (such as Bosch or NGK) for your car make (most major makes in the world). From there, it doesn't go by make year but by number of wires on the sensor. Then, look at the "SIGNAL +" and "SIGNAL -" line for that sensor type:


How to Read Your EFIE

The oxygen sensor gives its information to the vehicle computer by putting a voltage on its output wire. The voltage it produces is between .0 and 1 volts when measured against ground. However, when you're reading this voltage with a multimeter, it will show you a range of voltages of approximately .2 to .7 volts. The computer is able to read this constantly changing voltage, average it out, and adjust the fuel/air mixture accordingly.

Oxygen sensors have a warm up period before they operate properly. Some sensors just use the heat of the exhaust pipe to warm them. Others have an extra heater wire (and sometimes a separate heater ground too), used to heat the sensor more quickly.

Prior to the sensor becoming warm, it puts out an illegal voltage. The computer sees that the voltage is incorrect, and will ignore the data. The computer is said to be in "open loop". After warming up, the sensor will resume normal operation and will put out voltage as described above.

Notes by Ozzie:

1. When the sensor is cold, some Chrysler and Jeep vehicles add a higher voltage to the signal - wait till the engine is really hot.

2. If the O2 signal does NOT change when you depress the gas pedal, the sensor could be faulty, or it could be a WIDE BAND O2 sensor.

The EFIE has 2 test ports that you can plug the leads of your multimeter into. They are colored red and black, and you should plug in the leads with the same colors (for circuit board models, the red port is the same as the white wire, and the black port is the same as the green wire). When your leads are both plugged into the EFIE, you are reading only the voltage offset being produced by the EFIE. You are not reading what the sensor is putting out, nor what the computer is reading. You are only reading the voltage that the EFIE is adding to the oxygen sensor's output, before it gets to the computer's input. Note, that if the EFIE is turned off, then this reading will be 0 volts, as the sensor will be connected directly to the computer, and the EFIE will have no affect whatsoever.

So that is how you set the voltage that the EFIE is adding to the sensor's output. Both leads are to be plugged into the 2 EFIE test ports. To test the voltage that the oxygen sensor is putting out, attach your red meter lead to the EFIE's black test port, and your black meter lead to vehicle ground. If the car is running, then you should see a constantly fluctuating voltage between .2 and .7 volts on your meter. If you were to hook up an oscilloscope or other high speed testing device, you would see that the voltages actually range from 0 to 1 volts or so:


To test the voltage that the computer is receiving, plug your red meter lead into the EFIE's red test port, and attach your black meter lead to ground. Note that this will read exactly the same as the previous test if the EFIE is turned off. If the EFIE is on, you will read the voltage the oxygen sensor is producing plus the voltage being added by the EFIE. Let's say you set the EFIE to .25 volts. Let's also say that when reading the oxygen sensor in the previous paragraph, you saw a fluctuating voltage between .2 and .7 volts. When reading the computer's input voltage you would then see a constantly changing voltage in the range of .45 and .95. This is due to the .2 to .7 volts the sensor is producing, plus .25 volts that the EFIE is adding.

Note that now that we've added 0.25 volts (for example), there are
longer periods of "Too Rich" and shorter periods of "Too Lean"! (Ozzie)

In a practical sense though, you should never need to take these last 2 readings, unless you suspect that the sensor is malfunctioning. The only measurement you need to take is between the 2 test ports, so you can see what voltage offset the EFIE is producing.


The EFIE line offered by has previously just included the Single EFIE Deluxe and the Dual EFIE Deluxe. These have been, and remain, our flagship model. It is the recommended model to use for any hobbyist who is installing a fuel savings system in his car, and needs a device for controlling the output of the oxygen sensor.

However, there has been increasing demand for just the circuit itself, that can then be used in a combined electronics package, either created by the end user, or by another fuel saver manufacturer. To meet this demand, 2 new EFIE lines have been created. Both of these product lines will incorporate the same circuit board as our Deluxe models. There is no difference in the quality of the board or the parts. The only difference will be in the packaging as described and shown below.

EFIE Basic Series

The EFIE Basic Series will include both a single and dual version. It will not include the Deluxe series features of an enclosure, on/off switch, test points or panel mounted adjustment pot (pot = potentiometer, the screw used to adjust the EFIE). It is an EFIE circuit board, with an onboard adjustment pot, and approximately 5" of hook up wire for power, ground, oxygen sensor, and computer connections. The whole unit is rubber dipped in a spiffy blue colored material to protect its components and to insulate it electrically.

Pricing: Single EFIE Basic $49.95 --- Dual EFIE Basic $74.95.

EFIE Circuit Board Series

The second new line of EFIEs, the EFIE Circuit Board Series, is for the hobbyist or manufacturer that wishes to incorporate an EFIE circuit board into his own electronics package, and will supply his own connections and housing. It is a duplicate of the Basic EFIE series above, but is not dipped in rubber. It comes with an onboard adjustment pot, and approximately 5" of hook up wire for power, ground, oxygen sensor, and computer connections. You can see units of this type below.

Pricing: Single EFIE Circuit Board $44.95 --- Dual EFIE Circuit Board $64.95


EFIE Deluxe Series

Concurrent to the release of these new models, FuelSaver-MPG are incorporating a long needed price adjustment to the Deluxe line. The Singe EFIE Deluxe now comes in a spiffy gray colored case, and the Dual EFIE Deluxe will soon also come in gray.

Pricing: Single EFIE Deluxe $79.95 --- Dual EFIE Deluxe $114.95


NEW! Dual Wide Band EFIE

This product will work with all wide band oxygen sensors and AFR sensors. To be clear, it is the EFIE of choice for both 4-wire and 5-wire oxygen sensors. Also note there is a variation of the 5-wire sensor that uses 6 wires. This device will work with these too. This device will NOT work with narrow band sensors. For these, you must use any of our other EFIE models.

Pricing: $70 Dual - good for TWO O2 Sensors!
(no single version; if you have a single sensor, leave one side unused)


EFIE Installation Instructions

0. Install your fuel efficiency device

The EFIE is not intended to be a fuel saver by itself. You should install a device that is designed to get more energy out of the same fuel, such as a hydrogen gas electrolyzer, a fuel vapor production unit, or another device that gets more power out of the same fuel by increasing the efficiency of the burn.

1. Locate the oxygen sensor signal wire

The easy way to do this is to look it up in your Haynes, Clymer or Chilton manual for your car. I have also recently found a resource at whereby you can get your wiring diagram, and specific service manual information on your sensors. However, the information is not available for all cars and trucks. To help you find your wiring diagram at, follow the instructions found at Using the wiring diagram data, you can get the wire color of the signal wire, and hopefully gain access to it up in the engine compartment, where it routes to the computer.

If none of these options are available, you'll need to locate the oxygen senor and then locate the signal wire by testing. The sensor can have 2, 3 or 4 wires, and you have to know which one is the signal wire. If you have 4 wires they will be:

  1. Heater 12 Volts +
  2. Heater ground
  3. Oxygen sensor signal +
  4. Oxygen sensor signal ground.

If you have 2 or 3 wires, then you can have a common ground, or no heater wires etc. The simplest setup is a single wire, which is the signal wire and the sensor get's its ground from the exhaust pipe. You can use the following procedure to narrow down which wire is which:

  1. Disconnect the wire harness, turn on the ignition and probe for a wire that produces 12 volts. This will be the heater circuit.
  2. Next, find the 2 wires that produce exactly 0 volts. These will be the heater ground and the signal ground. The remaining wire should be your signal wire.
  3. Reconnect the wiring harness, then strip a little insulation from the signal wire and measure it to ground with the engine running. You'll get voltage readings constantly fluctuating between 0 and 1 volt, if you have the signal wire. Note that you have to let the engine warm up a bit before you will get these voltages from the sensor.
  4. Cut this wire at a convenient location for connecting the EFIE. We'll call the sensor side of this cut the sensor wire, and the other side of the cut, the computer wire.

Note: rarely an oxygen sensor wiring harness will have more than 4 wires. In this case, the sensor is possibly a "wide band" oxygen sensor. The EFIE has been reported to work with 5-wire wide band sensors.

Once you have determined which is the sensor's signal wire, you want to get it located up close to the computer. If you used a manual, or wiring diagram, you probably have already located the wire at the computer's wiring harness. If you had to figure out the wires at the sensor itself, then try to find the same wire at the computer's wiring harness. It should be the same colors, but test it with an ohm meter to be sure. Sometimes they use the same colors for different things. Even if it's a pain now, it's worth it to get the signal wire located up by the computer. This makes cutting into it and hooking up the EFIE much easier.

2. Locate 12 volt power and ground

You need to ensure that you have switched power, not power directly from the battery. You don't want the EFIE running 100% of the time. It's not that the unit couldn't run 100% of the time, it probably could. But it would slowly drain your battery.

Most of the fuel efficiency devices need switched power as well, and you can often piggy back onto them. Note that the EFIE draws negligible power. You can attach it to any circuit. The best choice for a voltage source is a fuel efficiency device, such as a Hydrogen generator (Electrolyzer). That way the EFIE only activates when the fuel efficiency device is turned on. Note that when power is shut off to the EFIE, or the EFIE's switch is turned off, the original connection between the oxygen sensor and the computer is re-established. If connecting to your fuel saver's power is inconvenient or inappropriate, just use any circuit that is accessory key switched. Your electrical diagram can come in handy here, and if you don't find another device to attach to, you can usually find a spare circuit in the fuse box (you may have to add a fuse). One installer used the oxygen sensor's heater power for his EFIE's power, and this is perfectly acceptable.

Ground can be the vehicle body, engine block or ground from another device, including the ground for the oxygen sensor itself. Just make sure that whatever you choose to use for ground has a negligible resistance (less than 10 ohms) when tested against the negative battery terminal of your car.

3. Mount the EFIE

You can use the mounting ears to screw down the EFIE to a suitable location on the vehicle body or firewall. Some people like to mount the device inside the passenger compartment of the car. There are some considerations about where you mount your EFIE that should also be reviewed:

  • The EFIE is not waterproof. If you mount it under the hood, you will have to take care to cover it if you need to steam or spray clean your engine. If this is something you regularly do, you may want to mount the EFIE in the passenger compartment where it will be protected.
  • If you live in a cold climate, where temperatures are expected to be below freezing a significant number of days per year, you will want to ensure that the EFIE is mounted where it will be warmed, either by the engine, or inside the passenger compartment. Below freezing temperatures cause the EFIE to come up to its voltage offset very slowly unless it is physically warmed. This is because it doesn't generate much heat of its own. In most cases this can be accomplished by mounting your EFIE in the upper rear of the engine compartment, close to the firewall, which will allow it to benefit from trapped engine heat. Newer EFIEs now come with jumpers that if set will cause the EFIE to generate more heat. These were intended for use in very cold climates. Find J1 and J2 on your circuit board. Set the following jumpers for increasing amounts of heat: J1, J2, J1 and J2.

4. Attach the wires

The EFIE multi-conductor wire has 6 colors: red, black, white, green, and (in the Dual EFIE) blue and brown. Connect the red to your power source. Connect the black to ground. Connect the green wire to the oxygen sensor. Connect the white wire to the computer. For Dual EFIE units, the brown wire goes to the 2nd oxygen sensor, and the blue wire goes to the 2nd sensor's computer line. Hopefully you've been able to locate all these wires up by the computer in an easily accessible location. But if so, be sure not to cut them too close to the computer so that you have plenty of slack to work with them.

You should solder them and use heat shrink tubing to insulate the connections from other wires. If you don't have heat shrink, you can use electrical tape. I personally always use heat shrink. It's more professional looking, and less likely to unravel later into a sticky mess.

EFIE Connection Diagram


5. Adjust the EFIE

You will now need to adjust your EFIE. They do not come from the factory with a particular starting voltage preset, so you'll have to set the initial voltage. I have found that .200 volts (200 millivolts) is a good starting point. The controls of the EFIE are shown and further described below:

EFIE Controls

The picture above shows a Single EFIE Deluxe, with the controls marked. The toggle switch turns the EFIE on/off, and the red LED glows only when the EFIE is on and has power. Note that when the EFIE is powered off, it makes the connection between the oxygen sensor and the computer, the same as it was before the EFIE was installed. If you ever have need to reconnect the oxygen sensor directly to the computer, just turn the EFIE (or Dual EFIE) off, and this will be accomplished. Also, if power is shut off to the EFIE, you'll get the same result regardless of which position the switch is in.

The red and black test points will accept and hold in place the electrodes (probes) from a multi-meter. The black point is attached to the oxygen sensor lead, and the red point is attached to the lead that outputs to the computer. Just push the leads in and they will be held in place by spring loaded clamps. With your probes in the two test points, you'll be reading the voltage offset being supplied by the EFIE, and this is the setup you need for EFIE adjustment.

The adjustment screw adjusts the voltage offset between the signal from the sensor, and what the computer "sees". Turn the screw in a clockwise direction to increase the offset, and counter-clockwise to reduce the offset, and your multimeter will be reading the offset amount. The signal adjustment potentiometer (or "pot" for short) is designed to turn 18-20 full revolutions. This is so that the voltage offset can be tuned to a fine degree of control. Adjustments as small as a few millivolts can be made.

Most computers will see 425 millivolts from the EFIE, plus the sensor's voltage as high all the time. In other words even when the sensor is putting out it's lowest voltage, when the EFIE adds 425 millivolts, the computer will think the sensor is reading high. The computer will think the sensor is damaged, because it reads high all the time, and will ignore its data. If this occurs you may or may not get a check engine light alerting you to the "defective oxygen sensor", but for sure your gas mileage will get very bad. So you should never operate your EFIE this high. The exact voltage is .45 volts to the ECU. Above that voltage is "high" and below that voltage is "low". The ECU must see transitions from low to high several times per second or it will "know" that the sensor is bad and then just start merrily adding gas.

It is possible to damage the adjustment pot by turning it past its lowest or highest values. However, I've turned them at least 10 full revolutions past the end with no ill effects. But there is a limit to how many times you can turn them, and I have ruined one once by turning one too far. The thing to do, is only turn them with your multimeter hooked up. When you get down below 50 millivolts, and further turning doesn't change the amount, stop. And the same applies at the top end of the scale. In actual practice you should never need to be at the extremes.

When it comes to making the actual adjustments to the EFIE for your particular car and fuel saver combination, I recommend starting out with 200 millivolts. The process of adjusting the EFIE is trial and error. If you're setting the EFIE above 350 millivolts you're starting to get pretty high. Watch for symptoms of too lean a mix such as rough engine, lack of power, "check engine light" coming on, etc. When these show up, adjust it back down until the symptoms go away. Note, some computers will accept an EFIE setting of over 400 millivolts. This is not the norm however, unless you take some of the actions discussed at the beginning of this article.

A couple of adjustment tips:

  1. If your "check engine" light comes on, you've likely set the offset too high, and the computer thinks your oxygen sensor is on the fritz (defective). This can also be caused by mis-wiring the EFIE, so make sure you're hooked up correctly.
  2. If you lose horsepower, you've got an incorrect setting, as fuel efficiency devices should increase horsepower proportionately with the increase in MPG (as well as decrease emissions).
  3. If you have a high temperature probe, run down the highway with the fuel efficiency devices turned off, long enough to get the engine up to full operating temperature, and note the temp of your exhaust pipe, near the exhaust manifold. As you increase your voltage offset, this temperature may increase. Don't let it raise more than 180 degrees from your initial test.

You will probably find adjusting the EFIE to be frustrating at first. When you turn the adjustment screw, the voltage starts raising (or lowering) and keeps on doing so long after you've stopped turning the screw. It can take up to 10 minutes or more for the voltage changes to completely settle down. I have learned to set EFIEs similarly to balancing a long stick on your finger. You have to turn the screw farther than you expect the final position to be to get the EFIE's voltage changing in the direction you want. Then when the voltage gets close to your target voltage, quickly start turning the adjustment screw the opposite way until the voltage stops increasing. Once the voltage is at your target value, then you just make small adjustments either way to get the voltage to settle down. But note you'll want to check the voltage some minutes later to make sure it hasn't continued to drift to a different value.

Another small detail that might throw you if I didn't point it out. When an EFIE is first connected to a vehicle and powered up, the voltage will go higher than normal, and then slowly settle back down. This is without changing the adjustment. This settling out period can take from 5 to 10 minutes or more. The primary manifestation of this is when you make your first voltage setting, then 5 minutes later find it has changed. This is normal. Just go ahead and re-set the voltage you want. After the EFIE is acclimatized to your vehicle you won't see this phenomena again.

These are the basics. If you run into trouble in your installation, post questions on the support forum, I can use the feedback to improve the guides here, as well as answer questions others may have as well.


Notes For Installing Circuit Board & Basic EFIE Models

This section is not intended to replace the EFIE Installation Instructions. It is merely trying to give you the differences between the circuit board models and the Deluxe models, so that you can use those instructions with your device.

The circuit board series and the Basic series are the same. The Basic series units have just been dipped in a protective, insulating material. These models are installed the same way (electrically) as the deluxe models. The directions that tell wire colors and what they connect to, are the same for the circuit board models.

Rather than using the switch on the Deluxe model, you will have to switch power to the red wire yourself. Another thing you'll want to address is a way to easily make connections to the white and green wires for making adjustments to the EFIE. In the Deluxe model, the white wire connects to the red test port, and the green wire connects to the black test port. Instructions that ask you to make measurements to these ports can be done by connecting to the white and green wires from your circuit board. For Dual units, on the 2nd EFIE, the blue wire connects to the red test port and the brown wire connects to the black one.

The pictures below show the EFIE circuit boards. Note that the photo of the Dual circuit board shows the parts for both EFIEs on the board, designated by the numbers 1 and 2. The final picture below shows the newest version of our Single EFIE that you will start seeing more of. It's the same design as the previous board, but uses surface mount parts which allows the board to be smaller.

Voltage Adjustment Potentiometer

The voltage adjustment potentiometer is the main adjustment for the EFIE. This is where the user adjusts the EFIE for his particular vehicle and fuel saving device(s). On the Deluxe series models this adjustment is mounted on the enclosure, so the circuit board will not have an R6 or R6A potentiometer on the circuit board.

Range Adjustment Potentiometer

This function has been discontinued. If you wish to find out more about it, please see "EFIE Range Adjustment Instructions" below. I recommend that this pot never be touched except by advanced users.

Dual EFIE Circuit Board

  • R6: Voltage Adjustment - EFIE #1
  • R6A: Voltage Adjustment - EFIE #2
  • R4: Range Adjust - EFIE #1
  • R4A: Range Adjust - EFIE #2
  • J1/J2: Heater Jumpers

Note that the wire colors for the Dual EFIE circuit boards are the same as for the Deluxe model. White/Green are used for EFIE #1, and Brown/Blue are used for EFIE #2.

Single EFIE Circuit Board

Heater Jumpers

We have found that extremely cold weather can adversely affect the functioning of an EFIE making it take longer to arrive at its set point. Folks that live in a climate where it is below freezing a significant number of days per year are advised to set these jumpers. J1 will provide moderate heating, J2 will provide about double the amount of J1, and setting both jumpers will provide the maximum amount of heat. Use both jumpers in New England for instance where it is too cold for human habitation from November to March each year. If you change the jumper settings, note your voltage setting beforehand, and then you'll probably need to re-adjust the voltage slightly after the change.

Test Points

The Deluxe series EFIEs have test points built in that you can plug your volt meter leads into for the purpose of setting the EFIE. Other tests can be done with these test points as covered in the section "How to Read Your EFIE" above. You will need to provide access to these test points yourself so you can set your EFIE and do these other tests. On the Single EFIE circuit board models, the white wire connects to the red test point, and the green wire connects to the black test point. For Dual models you also have a blue (or another white) that connects to the red test point for EFIE #2, and a brown (or another green) that connects to the black test point of EFIE #2. By giving yourself access to these wires, you will be able to follow any instructions given for the test points in the Deluxe series, by connecting your meter leads to these equivalent wires. Note: be sure these wires aren't allowed to contact other wires or ground, or the EFIE and your oxygen sensor will not work until the condition is corrected.


EFIE Range Adjustment Instructions

Important Note: The range adjustment feature has been discontinued for single EFIE models. It has proven to cause more confusion in users, than it has been of use, and it's just not needed in a modern EFIE. Voltages above .45 on an EFIE cannot be used. If the computer never sees a voltage below .45 volts, then it will "know" that the sensor is damaged and will ignore it. So, increasing the EFIE's range is not a valid use. Decreasing the range is also not needed as modern EFIEs are accurate across their entire range of voltages. Therefore the function has been discontinued. There are EFIEs in existing stock that will still have the range adjust pot installed, and this article will still apply to these. Also, it has been found that Dual EFIEs require calibration, and have therefore retained the pot that can be used for range adjustments. Finally, the range adjustment pot location has been retained on the circuit board. If some valid use for this feature comes up, then the board can be easily modified to again allow range adjustment.

EARLIER EFIE (they look like the photos below)

If you have an early version FuelSaver-MPG EFIE (photos below), follow these instructions:

Increasing the voltage range of the EFIE is not the only reason for changing the EFIE's range. If you find that you are getting your best mileage increases at .200 volts, for instance, you may want to decrease the EFIE's range to go to a maximum of .250 volts. The advantage is that the EFIE's front panel adjustment screw is more sensitive the closer you get to the EFIE's maximum voltage. By this I mean that you can turn the adjustment screw a full turn to increase the output by 20 millivolts when close to the maximum voltage, whereas it might take only a quarter of a turn at the bottom end of the EFIE's voltage range. This allows you to set your voltage offset very precisely, more easily. However, I run my EFIE at about .225 or so, and I have never changed it's range. This usage is not needed, and I don't particularly recommend it. But for you habitual tinkerers, this can be done.

Ok, so if you've gotten through the warning section and are still ready to go, here's how it's done:

1) Adjust your EFIE to it's maximum setting. The quickest way to do this is to back off the adjustment screw until your meter reads below 50 millivolts or so. Then turn it clockwise 20 turns. When getting close to the EFIE's lowest setting the voltage drops quickly, without the time delay you experience at higher voltages. At the top end you have to wait for many minutes to see if it is at it's maximum voltage, or, if you rush it, you may turn the screw too many times and damage the potentiometer.

2) Open the EFIE's case, taking care not to damage the wires and their connections. Then see the photos below for your model of EFIE, Single or Dual. Note that the bottom photos show the newest version of the circuit board. Find the range adjustment potentiometer on your EFIE's circuit board:

Earlier Versions of EFIE with Range Adjustment:

3) Turn the range adjustment potentiometer very slightly counter-clockwise to increase the EFIE's voltage range. Note that very small adjustments to this pot make a large change to the EFIE's range. Also note that you will have to wait for some minutes to find out what the full result of your adjustment is due to the large capacitor in the circuit.

4) When your meter reads the voltage that you wish to have as the top end of your EFIE's range, then adjustment is done. Replace the back on the case.

5) Re-install the EFIE into your vehicle and be sure to adjust it, as it's currently set to it's new maximum value.

NEWER EFIE (see photos below)

Increasing the voltage range of the EFIE is not the only reason for changing the EFIE's range. If you find that you are getting your best mileage increases at .200 volts, for instance, you may want to decrease the EFIE's range to go to a maximum of .250 volts. The advantage is that the EFIE's front panel adjustment screw is more sensitive the closer you get to the EFIE's maximum voltage. By this I mean that you can turn the adjustment screw a full turn to increase the output by 20 millivolts when close to the maximum voltage, whereas it might take only a quarter of a turn at the bottom end of the EFIE's voltage range. This allows you to set your voltage offset very precisely, more easily. However, I run my EFIE at about .225 or so, and I have never changed its range. This usage is not needed, and I don't particularly recommend it. But for you habitual tinkerers, this can be done.

Ok, so if you've gotten through the warning section and are still ready to go, here's how it's done:

  1. Adjust your EFIE to its maximum setting. The quickest way to do this is to back off the adjustment screw until your meter reads below 50 millivolts or so. Then turn it clockwise 20 turns. When getting close to the EFIE's lowest setting the voltage drops quickly, without the time delay you experience at higher voltages. At the top end you have to wait for many minutes to see if it is at it's maximum voltage, or, if you rush it, you may turn the screw too many times and lose track of where you are.

  2. Open the EFIE's case and then see the photos below for your model of EFIE, Single or Dual. Find the range adjustment potentiometer on your EFIE's circuit board. Note that the pots marked "Voltage Adjust" will not be on a Deluxe model EFIE. This is because the Deluxe version is adjusted by an external pot mounted on the box. Note that the Single EFIE in the photo has no range adjustment pot. But if a pot is in that location, that's the range adjustment.
  3. Turn the range adjustment potentiometer very slightly counter-clockwise to increase the EFIE's voltage range. Note that very small adjustments to this pot make a large change to the EFIE's range. Also note that you will have to wait for some minutes to find out what the full result of your adjustment is due to the large capacitor in the circuit.

  4. When your meter reads the voltage that you wish to have as the top end of your EFIE's range, then adjustment is done. Replace the back on the case.

  5. Re-install the EFIE into your vehicle and be sure to adjust it, as it's currently set to its new maximum value.

Advanced EFIE Design – BUILD YOUR OWN

Building your own EFIE will probably not be a big money saving proposition. In fact, if you give a value to your time spent on the project, and figure you should get minimum wage for that time, you will probably lose money. I'm not telling you this to discourage you from doing it. If you're a hobbyist and want to know the ins and outs of the device intimately, and take pleasure in building a project such as this, then by all means go for it. However, if you're just trying to save money, you'll be disappointed by the few dollars you save and the amount of hours of work it takes to do so. Okay, fair warning. If I haven't taken the wind out of your sails, then read on:

The EFIEs that are currently producing are based on the design originated by Eagle Research have produced the most advanced design of its kind that I am aware of, and if a better design existed somewhere, I'm pretty sure I would have at least heard of it. Their design is not patented and is open source, meaning anyone can build devices based on that plan without patent or copyright infringement.

CLICK TO ORDERHowever, since the cost of the plans is minimal ($9 last I checked), if you want to build your own EFIE, you must first purchase the plans/manual from Eagle Research. You can get them here:

I'm not giving out for free, the benefit of their research, when it can be obtained for such a reasonable amount. However, what I will give you is the benefit of my subsequent research into the design, and how to end up with an even better product.

Where to Find Your Parts

You can get many of your parts from Radio Shack. Resistors, diodes, and your LED (if used), wire and circuit board material can be used from Radio Shack. But the following parts, should not be purchased from Radio Shack, as you will get parts not made for an automotive environment. The voltage regulator, the 555 timer chip and the electrolytic capacitors will not be adequate. Radio Shack's versions of these parts are designed for use in temperatures from 0 to 85 degrees centigrade. Automotive parts are supposed to be rated for temperatures of -40 to 125 degrees centigrade. You may think that you won't be under freezing much and 85 degrees C is a pretty high temp. However, you don't want to even be close to the rated extremes of your parts. You want to be well within their operating minimums and maximums.

So get these parts from a larger outfit that has them in the automotive specifications ranges, such as DigiKey, Allied Electronics, Newark or Mouser. They cost, at most, a few cents more. Allied is probably the cheapest, but Digikey is nearly as low, and has a wider selection of the parts you will need. Check the ratings on them and get minimally -40 to 105 C, but preferably get -40 to 125 C. I've listed below, some Digikey part numbers that you can use.

The Voltage Regulator

I recommend using a 9 volt voltage regulator instead of 12 volts. The problem with a 12 volt unit is it drops 2 volts minimum from its input voltage. If your input voltage is 14 volts or more, then the output will be 12 volts. However, if the input voltage is 12 volts (for instance), the output voltage to your EFIE is going to be 10 volts due to the minimum 2 volt drop in voltage by the regulator. When your engine is running the alternator is charging the battery, and is producing about 13.5 volts, but it's fluctuating slightly all of the time. Therefore the output of the regulator will be 11.5 volts, and mirroring the car's voltage fluctuations. This must be eliminated for good steady EFIE voltage output. I use 9 volt voltage regulators and they are more than adequate for our purposes.

Note that there are 12 volt regulators that have lower voltage drops. These are rarer and generally more expensive. They are often labeled "LDO" for Low DropOut. These could also be used, but beware that some of these still have as much as 1.5 volts of voltage drop, which will still be quite close to having the same problem. If you find one with a .5 voltage drop, this would be adequate as well.

Specific Part Numbers

The only part you'll have trouble finding is the transformer. You'll probably just want to use the one I use in the EFIEs I manufacture. I get them from DigiKey and the part number is listed below. Its specs are almost an exact match to the one specified in the manual, and I've found that they are interchangeable. I've given a specific spec for the timer. I've found this timer to be a superior chip to others in the same family, and I recommend you use it. C1 should be 10 nF. R5 should be 3.3K. R4 should be about 4.4K, but I've found that substituting a 10K board mounted variable resistor here allows me to set the upper limit of the EFIE to a more precise value. This is even more important when building a unit with new parts. It allows you to fine tune the output.

I will give the part number of the variable resistor below, if you desire to do the same. Otherwise just use a 4.4K resistor.

C3 in the manual is a large electrolytic capacitor. Follow the specs in the manual, but make sure it's rated for -40 to 105 C. I don't think you'll find one rated to 125 C, so you'll have to settle for 105 C, which will be fine. I use a 220uF as I like that it comes up to voltage more quickly.

  1. Timer: Texas Instruments TLC555QDR - DigiKey: 296-10341-6-ND
  2. 9V Voltage Regulator: DigiKey: 497-4616-5-ND
  3. Transformer: DigiKey: MT4207-ND
  4. PCB Mounted Pot (R4): DigiKey: 490-2875-ND or 3296W-103LF-ND


Notes for Very Cold Climates

When using the EFIE in temperate climates, it operates normally and can be expected to maintain a steady and reproducible voltage offset. However, in very cold climates, such as in locations where it is below freezing a significant number of days per winter season, temperature becomes a consideration. If the EFIE cannot warm up to a normal room temperature, it will read lower than it will when warm. As the EFIE draws almost no power, it also doesn't generate much heat, and cannot warm itself when in extreme cold weather. In this case it will generate a fraction of its normal offset voltage. This can be almost completely handled by merely mounting the EFIE to the rear of the engine compartment, where engine heat tends to be trapped by the firewall, even when driving down the highway. Of course you can mount the EFIE inside the passenger compartment, where it will be heated.

Using the EFIE Manual from Eagle Research, and the design modifications above, you can create the most advanced unit of its kind available anywhere. If you wish to buy your EFIE pre-made, you can get them from Both Single EFIE and Dual EFIE models (for cars with 2 oxygen sensors) are available.

If you have trouble building your EFIE or need to clarify these instructions, post your question at Your reply will most likely be from me, and I answer up there quite quickly. Good Luck!


Additional data by Ozzie Freedom:


The auto engineers call it "Malfunction Indicator Lamp" or "MIL". For us, it's simply the "Check Engine Light" or "CEL". Depending on the vehicle you're experimenting with, the check engine light may come on. Your ScanGauge (or another scanner) may help in identifying the error code (see error guide below). However, assuming that your vehicle is in good shape, the check engine light will probably come on for one reason: too good of performance!

In Water4Gas, when we talk about "good performance", we mean better (higher) gas mileage and better (lower) emissions. What happens is, sometimes the light comes on because the ECU detects "unusual activity" in terms of performance. Newer cars, by the way, are more sensitive than older cars. You can try resetting your ECU by disconnecting the battery (more details below) and tweaking the settings of your system so they don't trigger the light.

However, some vehicles are too sensitive about emission standards and will display the check engine light no matter what you do. Some cars get check engine lights after a mere muffler change! This does not mean that your vehicle is malfunctioning. It only means that the ECU has detected a change in EMISSIONS and FUEL CONSUMPTION. Erroneously, better performance is detected as a faulty condition.

I am sure the auto designers, as well as many of their engineers, are aware of their design error, but their hands are (currently) tied. In the near future, all auto makers will have to yield to Water4Gas systems of all types and models, including their own manufacture of such systems (which will then come with every new car). In the meanwhile, we have to realize that when the light comes on, it is an indication that our system has created a detectable change!



First of all, why would you want to disconnect the car's battery? Well, some people do it in order to erase the "adaptive memory" of the ECU, so it can re-learn the correct settings for fuel economy. We want to adapt to the better combustion due to the presence of HHO, and everything that is now occurring as a result – including lower than expected fuel consumption.

First let's take a look at 2 major problems with merely disconnecting the battery:

1. On some late model vehicles, disconnecting the battery may result in driveability or other problems. When you disconnect the battery from the car, power is lost to the ECU – but also TO OTHER ONBOARD MODULES. This resets the ECU back to its factory settings. After re-connection, it will take the ECU's adaptive memory some time to re-learn the CORRECT settings. The transmission will need to re-adjust in order to shift properly, so gearshifts may seem different at first. The re-adjustment process may take 10 to 50 miles of driving.

2. Other car modules might also forget their learned settings. Such settings includes the electronic modules that control the air conditioning system, power seats (especially if those have individual settings for each driver), power windows, power mirrors and sunroof, radio stations and other settings in the sound system. Certain anti-theft or keyless entry systems have adaptive memory that relies on the vehicle's battery to keep their settings. Some of these electronic modules may not work properly after the vehicle's battery has been re-connected. They may even require a repair procedure (scan tool to release the error codes or standby mode), which might turn costly depending on the vehicle model and dealership.

Therefore, you should check your vehicle owner's manual for precautions regarding disconnecting the battery.

The SIMPLE solution:

  1. THIS IS NOT A MAGIC SOLUTION – the first step is to properly install and tune any adjustment device you have chosen (such as EFIE or MAP Sensor Enhancer)
  2. Warm up the engine, or do this after a ride when the engine is warm and has its normal operating conditions.
  3. Do NOT disconnect the battery from the vehicle. Disconnect ONLY THE ECU PLUG (OR PLUGS).
  4. Leave it unplugged for 10 minutes.
  5. Connect the ECU plug(s) back on.
  6. Start the engine for 2 minutes, then turn it off.
  7. Repeat the previous step 10 times.
  8. Now the ECU will start learning the vehicle's behavior and performance just as if it was a brand new car. Since it has a new performance range with HHO, chances are that the computer will not negate the newly acquired gains in economy and power range. It will learn "to live with it"! This learning process may take, approximately, from 10 to 50 miles of driving.

This solution does not solve problem number 1 above, because the ECU still needs to learn things like proper gearshifts. But it eliminates problem number 2 (radio memory etc). However, problem number one is not really a problem. We actually want the ECU to forget its "wrong" learning of the past - and learn anew. There may be one or two adaptive settings there that would be the same before and after HHO has been introduced, but for the most part, we want the settings to be refreshed.


sensorFor your general information, you can also build yourself an EFIE alternative from free plans known as "D17". The plans can be found on the Internet:

Just like Mike said about the hardship of building the EFIE yourself, it took me a long time to build my D17, mainly since it it was hard getting all the parts in my town. Construction itself was fun but not time effective, so I decided to give up mass production of D17.

This is a workable option if you have good experience with electronics and attention to details, because it's more complicated and needs to be debugged in case of mistake or malfunction (often happens).

The switch that I've installed toggles between FULL RICH and ENHANCED MODE. In the enhanced mode I can dial down up my MPG - using the knob. This knob is not a variable resistor. It is a rotary switch, offering only six positions between maximum rich and maximum lean.

The picture below shows the device I've built from D17 plans:



For me, the hardest part in this project was finding the components. However, online electronic stores such as and should be able to supply you with just about everything needed for this project. Local electronics supply stores may carry all parts if they are really big stores, or if they specialize in electronic components. Otherwise, you'll have to collect the components from several sources.

NOTE: I found out that D17 does not work as described in the Internet plans. To fix it, replace the input resistor (sensor side) from 1M to 10K Ohm.

Pete McGregor from Australia sent me his own design for EFIE, based on a DC/DC converter. His remarks are below the diagram:



  • T1 is made from 3 lengths of varnished copper wire, all approximately 7 meters (23 ft) long, diameter 0.2 mm. All three wires are wound together onto a PLASTIC sewing machine bobbin.
  • The 20K variable resistor must be a MULTI-TURN trim pot.
Article Details
Article ID: 262
Written by: Mike Holler, Mike Kehrli, Ozzie Freedom, Pete McGregor. EFIE originally developed by George Wiseman, further developed by Mike Kehrli to stabilize temperature.