Is an O2 Sensor necessary on a 3.2 DME?
 

As discussed in the "Sport Muffler" thread, I recently installed a hybrid muffler that consists of a cat-bypass pipe and an Edlebrock muffler - all in one on my '87 coupe. During the installation I could not get the O2 sensor off my stock system. My mechanic, Steinel's, said he would most likely break it if he tried to remove it. He said just run the car without one and it will run better. He said the sensor is just there to richen the mixture and then lean it out to "ignite" the cat and that the DME does not use the sensor to tune the car but only to keep the cat working. He said this is not true with the later cars as the O2 sensor does play a role in tuning the mixture.

Is this all true? My concern is that my car, while it runs great now, will run unnecessarily rich and may promote the infamous premature valve guide wear. Any thougtht?

TIA
Pete Brown
'87 Black Coupe

You do indeed need the O2 sensor as you specified in the last sentence, and more reasons.

BTW: How does that Edelbrock muffler sound?

On a Motronic system, (or most EFI systems for that matter) the O2 sensor is the #1 sensor to monitor fuel mixture. The ECU uses various inputs (MAP or A/F, TPS, etc) to determine the proper fuel mapping, and the O2 sensor is the only way it knows "how good it did its job", and adjusts accordingly. Can it run without one? Sure,... but depending on how the sensor failed, (shorted, open, stuck, etc) will determine how much fuel it will get. Most have some type of "limp in", or "open loop" default programming. You DO NOT want to run a car very long without one. I'd be taking my car elsewhere to get it repaired. It has nothing do with the Cat. Newer cars have two O2 (some have 4 or more) one before each Cat and one after it. The one after it is there only to monitor cat effeciency, not fuel mapping. I have heard alot of them, but never "to ignite the cat"!

Yes you need your O2 sensor. Without it you will lose about 4 hp across the powerband. I had two dyno runs on my '87 last year, the first with the sensor registered 220 hp, without 216. Again the loss was through out the power band and not only at peak.

Pete
02 due on May 2