EFIE Information Page

Last Updated: Jun. 07, 2014

We know vehicle electronics can be a little confusing at times, with trying to figure out what device is best for your vehicle. This is a supplemental article about the EFIE devices we offer. If you are looking for the Installation Manual, or if you have any questions at all about this article, please do not hesitate to Contact Us.

Please use the list of links below to help navigate the page.

What Is An EFIE?

EFIE stands for Electronic Fuel Injection Enhancer. The purpose of the EFIE is not to provide fuel efficiency, but to make it possible for a fuel efficiency device to work. The EFIE is designed to manage the Oxygen Sensor readings to the ECU (Environmental Control Unit). Basically, what happens when you install a fuel efficiency device, is that the emissions computer thinks something is wrong. There's nothing wrong, however; the added HHO to the engine will read as more output through the emissions sensors (in this case, the oxygen sensors). The ECU will then make fuel injectors adjust to what the engine now believes is a "lean" air/fuel ratio. It's only trying to adjust for this "wrongness". Without the EFIE, the actions the ECU takes is based on the oxygen sensor data, negating the efficiency increase that would have been realized by the efficiency device.

One fundamental point about an EFIE is that it is not a fuel efficiency device, on it's own. If all you did was add an EFIE to your car, with no other fuel efficiency system, you really won't see any difference in fuel economy. What happens , now, is you are just fooling the vehicle's computer and making it run off-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. In most cases, just the EFIE device, alone, may actually give you worse fuel economy.

The mechanics of this are that any time you add a technology to your vehicle, that improves the efficiency of combustion of the petroleum fuel you are burning, one of the results of this process is that there will be more oxygen appearing in the exhaust. When the sensors "see" this additional oxygen the computer interprets this as a "lean" condition, and incorrectly adds more fuel. This can severely reduce the mileage increase you will get from your combustion enhancement technology.

The EFIE solves this by adjusting the oxygen sensor's signal, to the ECU, 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.

Which EFIE Do I Need?

Before we get into the details, please keep in mind that we recommend the Narrowband Series EFIEs for about 90% of all vehicles. We recommend these units for virtually all American cars, all foreign cars older than 1997, and most foreign cars after 1997. In the rest of the article we will cover why, and also the exceptions to the rule.

Basic Types of Oxygen Sensor

There are 2 basic kinds of oxygen sensor. They are called "narrow band" and the more modern, and superior, "wide band" oxygen sensor. The most important distinction is which of these 2 types of oxygen sensors you have. An EFIE made for one type will not work on the other. If you have any doubt about this point, you can contact us and let us look up your vehicle to be sure.

It is often easy to figure out what type of sensors you have. Is your car pre 1997? Then it's narrow band. Is it an American Car? It's narrow band (we've now seen a few wide bands in 2009 American cars, but none before that). If it is a German or Japanese make and was built after 2000, then you should suspect that it has wide band sensors. Actually a very few cars started using wide band sensors in 1997, but it is only after 2000 that they are used with any regularity. But here's another test: Does the sensor have more than 4 wires? If it does, then its a wide band sensor. Note that Toyota and Honda uses a 4-wire wide band oxygen sensor. All other makes use 5-wire or 6-wire wide band sensors.

Here's another way to tell: Open your hood. Now look up. Do you see a sticker up under the hood with technical data about your vehicle? Often if you have wide band sensors, they are noted on these stickers for the mechanics. Note that it may be called an AFR (Air/Fuel Ratio) sensor, or AFS (Air/Fuel Sensor). These are all synonyms for a wide band oxygen sensor.

One other point: If you have wide band sensors upstream of the catalytic converter, you will still have narrow band sensors downstream. As of this date (2009), we have never seen wide band oxygen sensors being used downstream.

Number of Sensors

The next point is, "how many sensors do you have?". V-6, V-8 and larger, usually have 2 sensors that are upstream of the catalytic converter, one on each exhaust manifold. Further, they will have 1 or 2 downstream sensors as well. Note: some pre-1996 vehicles don't have downstream sensors. Vehicles with 4 cylinder engines usually have 1 upstream sensor, and 1 downstream sensor. You will occasionally run into some oddball configurations that vary from these, but these are the usual configurations.

We recommend that you treat all oxygen sensors regardless of whether they are upstream or downstream. Many manufacturers are now using the downstream sensors in their air/fuel calculations, and others are using them to check the function of the upstream sensors, causing odd trouble lights and poor mileage gains. Because this has become so prevalent, these EFIE units are designed to include EFIEs for both the upstream and downstream oxygen sensors. These products include the correct combination of EFIEs to treat both your upstream and downstream sensors.

For instance, the Quad Narrowband EFIE has 2 digital EFIEs for treating 2 upstream narrow band oxygen sensors, and 2 analog EFIEs for treating 2 downstream sensors. Using analog EFIEs on the downstream sensors was not a cost saving consideration. We have found that analog EFIEs work better on downstream sensors, while digital EFIEs are clearly superior working on upstream sensors

For those who have wide band sensors, we have a similar product, theQuad Wideband EFIE, where 2 Wideband EFIEs for the upstream are combined with 2 Analog EFIEs for the 2 downstream sensors. Both the Wideband Quad EFIE and the Quad Narrowband Digital EFIE, come in a version designed for 4 cylinder engines too. These have 1 EFIE (either Wideband or Digital) for a single upstream sensor and a single analog EFIE for a single downstream sensor.

Finding Your Signal Wire

You May Not Need a Diagram

The following document has the wire colors for the oxygen sensor for many models of car. We've found this Oxygen Sensor Wire Colors supplemental .pdf file to be particularly useful. Be sure to magnify the image by clicking in it, for clear reading. Once you have identified the signal wire on the sensor, then go back to where the sensor wires plug into the vehicles wiring harness. You need to do this to find out what colors are used for the same wire in the vehicle's wiring.

Repair Manuals

When buying a new or used car, getting the vehicles repair manual for it is always a good idea. Included in these manuals are the wiring diagrams and the color codes for all of the sensors. There are several to choose from Haynes, Chilton's, Clymer and others will all be similar with the information contained. But we have always found Haynes to be the most informative. These manuals cost $20, which is generally money well spent. They are usually available from your local auto parts store, or you may even find a copy off of eBay. There are a few makes and models that they don't cover, but they have a manual for most vehicles sold in the US. For vehicles outside of the US, you can also ask an auto mechanic or your vehicles dealership. You also might want to try finding your manual on eBay, or even see if your local library has it.


Next, see if you can find your diagrams for free AutoZone's website. AutoZone posts wiring diagrams for many cars and trucks for free. They also have a vast amount of repair information, including diagrams of part locations, detailed instructions, etc. If you don't have a repair manual for your car, you can just about get by with this, all by itself. However, not all cars are covered by this service. You'll just have to look and see if yours is.

To see what they have for your vehicle, go to the AutoZone. Select "Vehicle Page" from their site. Then select the Year, Make, and Model, of your vehicle. You may have to register, as you may not get all of the same resources without registering. However, by registering, you can save your car's information. So, when you login again, all of the information is there without having to re-navigate the car selection.

If you have a hard time finding the wiring diagrams, to specifically find those, do the following:

  1. Locate your Vehicle, Year, Make, and Model
  2. Select "Repair Info" at the left side of the screen
  3. Then select: "Vehicle Repair Guides" -> "Chassis Electrical" -> "Wiring Diagrams"

You should be able to locate the ECU diagram, oxygen sensor signal wires, all of the other sensors etc., including the MAP (Manifold Absolute Pressure) sensor, if it has one. For some vehicles you’ll find which kind of sensor (DC voltage or frequency type), and even resistances = what pressure in the ECU. The same goes for it's entry on the CTS (Coolant Temperature Sensor), what temperature = what resistance from the sensor. This will help you enormously if you need to do adjustments to any other sensors, for any reason.

Mitchell's Online Repair Manuals

If the above resources weren't able to help you, then you can get your wiring diagrams from Mitchell's Online Repair Manual web site. The way to do this is to sign up for their 1 week subscription. This is a one-time payment, and entitles you to access for 1 week. You'll then want to copy the wiring diagrams and save them for your future reference.

Note: Unfortunately, this service is only for models that are sold in the United States. Models that are not sold here are not covered by this service. This includes domestic manufacturers, that make models sold only in overseas markets, but not in the U.S. If you are aware of a similar service that supplies diagrams for foreign makes and models, please email us, and we'll update this article with the information.

Once you've logged in, you'll do the following steps:

  1. Press their "Subscribe" button, then select your vehicle, and finally pay them to join their service. You only need to sign up for 1 week.
  2. Select "System Wiring Diagrams"
  3. Go down until you find the section "Engine Performance Circuits"
  4. Copy these diagrams. All of your sensors will be included in this section.
  5. If you want any other diagrams, copy and save them as well.

The Digital EFIE: How it works

First, lets have a look at how oxygen sensors work. Have a look at Figure A below. Here we have a graph that is a representation of the voltage output of a typical oxygen sensor while the engine is running. Note, that this is only an approximation of a real voltage graph. A real graph would be much more jagged and would not be so regular as this one. But I'm using this graph to make it easier to visualize the concept of what the sensor is doing.

Narrow band oxygen sensors don't tell the ECU what the air/fuel ratio is. They only tell if the mixture is rich or lean. The line that is marked ".45" volts denotes the make/break point for the sensor's voltage output. Any voltages that are higher than .45 volts is considered to be rich, and any voltages that are less than .45 volts is considered to be lean. When the sensor produces .45 volts, that is considered to be the correct air/fuel mixture which happens to be 14.7 to 1, air to fuel (by weight). The trouble with narrow band sensors is that they can't tell the ECU how rich or how lean the mix is. They only tell the ECU "rich" or "lean". Therefore, in normal operation, they are constantly changing voltages similarly to the graph in Figure A.


Now look at Figure B. The blue line in this graph represents how an EFIE changes the voltage graph of the sensor. As the sensor produces its voltages (as represented by the red graph), the EFIE adds additional voltage. We are showing an EFIE set to 350 millivolts (.35 volts). Therefore the output of the EFIE that goes to the computer will be the voltages in the blue line on the graph. Because higher voltages mean a richer mix to the ECU, the ECU will then lean the mix when it "sees" these "richer" mixture signals coming from the oxygen sensor.


Almost all EFIE designs that are in use today work like the above graph, by adding a voltage to the output of the oxygen sensor. While this approach does work, and has been the only solution available for many years, it has 2 problems that make it not the ideal design:

  1. There is a definite limit to the amount of voltage you can add. Notice that if we added .5 volts in the above graph, that the blue line would never dip below the .45 volt line. This is an illegal condition and the ECU will quickly stop using the oxygen sensor if it never sees the voltage transitioning from rich to lean. In actual fact many ECUs need to see voltages lower than .45 volts before it will consider that the mix is lean, and so often you can't set an EFIE higher than 250 millivolts or so without throwing engine error codes.
  2. It takes a relatively large change in the voltage to make a small change in the air/fuel ratio. This wouldn't be a problem in itself, but coupled with the fact that we can only add a limited amount of voltage, this causes an end result of a small change in air/fuel ratio.

There is one other approach in EFIE design in use today, and that is to use an amplifier. Instead of adding voltage to the sensor's output, EFIEs of this type will amplify the signal. This, in effect, multiplies the signal. This is a better approach in that the lower voltages are not increased as much as the higher voltages, and you should be able to shift the air/fuel ratio further than with a voltage "adder". However, it is still limited to the amount it can shift the voltage before all voltages are higher than .45 volts. Also, the amplified voltages at the top of the graph can get quite high, possibly high enough that it will set off alarms in the ECU.

Enter the Digital Narrowband EFIE

There are other EFIE designs being marketed as "digital". In each case, as of this writing, the only thing digital about them is the pot used to control the EFIE. It's a digital pot and will have one of 64 or 128 resistance values, or possibly more depending on the resistor chip design. While this is cool, it makes no difference in the operation of the EFIE. It will still be operating like one of those described in the section above.

Our new Digital Narrow Band EFIE operates completely differently from any other EFIE made. Our new EFIE is called digital, because it's output is either on or off. Or in other words is either high or low. Or to put in terms the ECU will understand, the output will be either rich or lean. Or to put it in terms of voltage, the output is either going to be .100 volts or .900 volts. This is perfectly acceptable to the ECU and tells it exactly what we want it to see. But because it's output is only one of 2 states, we rightfully call this device a "digital" device.

So how do we know when to switch from the high state to the low state? We have a comparator in the EFIE that "decides" when to switch states. If the EFIE were to be set so that there was no change in air/fuel ratio, the comparator would be set to .45 volts. This would mean that if the voltage coming in from the sensor were below .45 volts, the output would be low, and likewise if the voltage coming in from the sensor were above .45 volts, the output would be set to high. This would cause a flat response in the ECU where it would provide the same air/fuel ratio as if the EFIE were not involved.

To lower the air/fuel ratio we need to make the mix appear richer. In order to do this, we make the EFIE transition to a high output even though the input is below .45 volts. In other words, instead of using .45 volts as the switching threshold, we use .20 volts (see Figure C). By adjusting the pot on our new EFIE, we are adjusting at which voltage the comparator will use to determine if the output should be set to high or low. In the graph below, we show 2 comparator voltages for comparison. At .45 volts, we can see that the output will be high about 1/2 of the time. This is the same as it would be without the EFIE. Now notice the line at .2 volts. By setting the EFIE's comparator at .2 volts, the EFIE output will be low for about 30% of the time and high about 70% of the time. This will make the air/fuel mix look richer than it is, and the ECU will respond by leaning out the mix.


Note that 0.200 volts is probably too low for your vehicle. You will probably not need to set it this low. We only set it here to make it easy to see the principal involved with our new Digital EFIE. An actual setting would probably be closer to 0.300 - 0.325 volts.

Note: When downstream sensors need to be treated, do not use this device. Use an older style, voltage adding type of EFIE. The reason for this is that we're not certain how the downstream sensor information is used by the ECU. In some cases, we have read the voltages from downstream sensors and they don't jump up and down as shown in the graphs above. We've seen them just float around in the 0.200 to 0.300 volt range, not changing much. This is not the behavior that the Digital EFIE was designed for. It may work fine. But we prefer that the ECU just see the same behavior, but shifted up a bit, the way a voltage adding type of EFIE will do. Any of our Narrow Band EFIEs that aren't labeled "Digital" will work for this application.

Using this device, some people have been able to lean the mix to the point that the engine will die. However, in some cases, it is still necessary to do other treatments to get the leaning results needed. For instance many ECUs use the downstream sensors as part of the air/fuel calculations, and many more will use the downstream sensors to verify the upstream sensors and throw odd engine errors. In these cases, downstream EFIEs are needed to get the needed results. That's why there is also a Quad Digital EFIE. It has 2 digital EFIEs for the upstream sensors and 2 analog EFIEs for the downstream sensors. This will give you the optimum treatment for each sensor, and is the most powerful solution we've seen yet for optimizing your engine for use with HHO or other fuel combustion enhancement technologies.