I’m at a total loss for this problem.
He disconnected the battery overnight and unplugged both O2 sensors. It ran exactly the same. He had not disconnected the AIR pump line in the exhaust so he did that and retested it. Same thing three cylinders are dead rich one is very near .


I don’t where to go now.

This issue started when the left cat was replaced. It had developed a very rich condition on the left bank , driver side. He said the Cat was bad so the left Cat was replaced .

Right here was when the issue switched to the right bank. This is the puzzle piece. Why did the condition switch sides?
This has been the question constantly asked through out all the testing.

We then replaced the right Cat, since the car had 110 k on it. I still have the old one.

I’m going to get the car back and run EEHACK as y’all have noted.

Question here is resetting the BLM. do I do this after hooking the battery up but before starting thr car or while the battery is disconnected?.


The compression test was very even. I don’t have s number but he said it was good. I would think a cracked piston might show low on that cyl. But I have take sbc apart that ran fine with several cracked pistons.

I asked awhile ago above if very bad valve seals and guides might be causing this.

Byron