Just a curious question... Downstream o2 was known to be bad, didnt throw a code. Removed cat, still no CEL. Replaced with new o2, no CEL (should show threshold below whatever because the cat is removed ATM). Unplugged it and its still not throwing code? Is this normal?

 

The fact that you said you unplugged it and no code right there should be a red flag. I mean the code might take some drive cycles. But if it's not popping, sounds like it was tuned out.

 

Is there any other possibility? The car doesnt seem modified and especially doesnt seem like the PCM has anything modified. I have no way of actually looking into the PCM but things like shift points all seem stock.

 

So, if you unplug the rear O2 sensor and go driving around, I am going to be almost certain it will pop a code (such as a voltage problem or some other code due to a lack of a reading from the rear O2). I would also see if you can scan readings from the rear O2 and what the PCM has to say about it.

 

Ive actually been driving it everywhere lately since it runs well. Ive unplugged the rear a few times just being curious. Have probably driven 2-3 hours with it unplugged. With it plugged in tho, its acting normal. Bouncing from .1-.9v. I did noticed that at some point the wires were cut and re-spliced.

Is there anything else I can look at to determine whether the PCM has been altered?

 

Unfortunately, the only way I know to prove if the PCM was altered would be using a DHP PowrTuner or HP Tuner to read the file from the PCM and look at it. Outside of that, I don't know a way with typical scan tools to prove it. I mean, if you wanted to pull the PCM and pay to ship it back and forth, I can do all that on a bench.