I have had a problem with my 97 Z for the last year and every once in a while I get back into wanting to fix it. Anyway basically the car will not run very good at all when the car warms up and switches into closed loop mode. The more you drive like that the worse it gets until SES starts flashing and car barely drives. My car is OBD2 stock and I have a tuned OBD1 in there. It does the same thing when going into closed loop with the OBD1. The only thing on the car that I have not messed with are my rear 02 simms which I know go bad very often. I am wondering that even though I am now running an OBD1 computer which dont use rear 02's, could the computer be reading off them since they are on the car and plugged in? I would like to try 2 new simms and run my OBD2 again but dont have the money to buy 2 new ones.
Thanks for the help,
James

 

I doubt there is even any circuitry in the PCM to allow it to read the rear O2s. The OBD-I PCM should ignore them.

 

All the rear 02's do is tell the computer if the cats are working properly or not, so I doubt thats your problem.

 

Even with OBD2 the rear O2s can not effect engine management, like speed_demon said they are only a tattle tale for the cats. So they are not the problem.