ok so i installed a air-fuel ratio sensor to my 89 toyota pickup with a 90 7mgte engine and the meter is jumping from lean to ideal rapidly when im cruising. when i accelerate it seems fine and when i let off the gas it completely disappears. i have a video of what im talking about. if anyone has any ideas i am happy to hear them.

[YOUTUBE]http://www.youtube.com/watch?v=DVSqm6P3Tnc&feature=youtu.be[/YOUTUBE]

 

Is this a wide band unit or a narrow band? I assume narrow band...

Narrow bands (the kind you tap into the O2 sensor wire) are known for being "inaccurate" like that. It's not actually "inaccurate", but what's actually happening is that it's reading the voltage fluctuation pattern (cycle). During normal operation, the voltage will cycle from ~0.10v to ~1.0v very rapidly, and must reach a certain voltage (usually about 0.8v), and it must cycle a certain number of times per second (also called "cross count") to be considered a "good signal". The faster it does this, the more samples and more accurate they can be considered to be. They do slow down over time as they wear out. The reason for the cycling is because the ECU is constantly and instantaneously altering the air fuel mixture for various reasons to help the combustion process as well as fueling the "engine" inside the catalytic converter to convert exhaust gasses, which is a whole other topic.

When you are on-throttle, it reads a solid number because of the feedback from the sensor seeing a constant applied fueling amount (the ECU isn't controlling it as much like at a cruise). When you are off-throttle, it disappears because the mixture goes so lean (which is normal) because the injectors are all but shut off when the throttle plates close, and the engine is typically running on an idle air control valve circuit. Even widebands will show this.

Wide band units are much more accurate and require their own wideband O2 sensor. Most wideband units are made up of the sensor, a controller, and a readout gauge. Some units (like the AEM UEGO) are built together into one nice little package. Others (like the Innovative Motorsports units) are separate piece you can customize to what you are trying to do.

Hope that helps!

~T.J.