Fuel Saver

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 it's 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 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 or a Chilton's manual for your car or truck, preferably Haynes as these are generally more informative. If you don't have a wiring diagram for your vehicle, then see this article: Wiring Diagrams. 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. You can find out about it here.

If you read the Installation Instructions, 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 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.


I hope this page hasn't confused you. But it's best to start digging in and finding out what you really have under the hood, so you don't end up purchasing an EFIE that you don't need or can't use. If you still have questions about this you can post them at: www.fuel-saver.org, our support site. Just press the "New Thread" button, and ask your questions there. I answer up there quite quickly. The important thing is that you get your questions answered and are able to move forward with certainty on your project.


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