I just installed the Apexi cat-back on my '97 and there was no hole for my O2 sensor behind the cat. I have it wired out of the way just above the pipe right now. No check engine light. I was wondering if I even need it. What exactly does it do and does it affect fuel/air mixture or the ECU? Anybody have some tech knowledge on this? Thanks.

 

The rear Oxygen Sensor monitors the performance of the main Catalytic Converter. It has no influence on the air/fuel ratio. However, I would have expected the Check Engine Light to go on. Don't be too surprised to see it go on in the next few days.

 

Yep....The Check Engine light should come on as part of the OBD II system.

 

Is there a way to fool the car into thinking the O2 sensor is there and working?

 

Yes, but not easily. There are Simulator Boxes which can be used to mimic sensor signals. These are useful diagnostic tools. I think they are expensive... don't know the price... don't have one.

A "savvy" electrical engineer could measure the signal coming from a healthy rear Oxygen Sensor and build a circuit which generates that signal. It is a sinusoidal waveform which varies between a low in the range of 0.0 - 0.3 vdc to a high in the range of 0.6 - 1.0 vdc. I don't know the frequency, but believe it to be low (10 hz or less).