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Old 11-01-2015   #1
89 GTA
Join Date: Nov 2015
Posts: 11

Exhaust System Help

I am new to the forum so forgive me if this is an old topic.

Just purchased an 89 GTA with the 5.7L. The guy I bought it from put a custom exhaust system on it and it has a service engine light on the dash now. He did not put cats back in the exhaust. I am assuming, the code is due to the lack of an oxygen sensor or the missing cats? Or both? It runs great, just want to get rid of that warning light.

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Old 11-01-2015   #2
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Join Date: Mar 2015
Posts: 280

Re: Exhaust System Help

Yes and no.

No oxygen sensor? Yes, this would cause a light. The computer is looking for this input, and not finding it. There's no good reason not to run one.

No cat? No, on an older OBDI, single O2 sensor vehicle, the absence of the cat cannot be detected by the computer. Your car should have a single sensor ahead of the cat. Therefore, it does not "see" the cat, or it's effect on exhaust gasses. In newer cars with OBDII, there is a post-cat O2 sensor, so it can "see" how efficiently the cat is working, and will set a light if there is no difference between the pre-cat O2 (cat either missing or inop.) and the post-cat O2.
1988 Pontiac Trans Am
POCI #72200
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Old 11-01-2015   #3
89 GTA
Join Date: Nov 2015
Posts: 11

Re: Exhaust System Help

Thanks. That's what I had expected. I'll have to get the O2 sensor installed.

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