failed emission
Thread Starter
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Joined: Feb 2006
Posts: 91
Likes: 0
From: Peoria AZ
failed emission
I have a 93 LT1 with 50,000 miles. Failed Arizona emission test. Both Carbon monixide and hydrocarbons failed. NOX passed. I have no codes in the computer and service engine light is off. Anybody know what I might look for first, or should I go to dealer?
Instructor
Joined: Mar 2005
Posts: 174
Likes: 3
From: Yorba Linda CA
Make sure the engine is hot (drive 20 miles) before you take it in for testing. I found that there was a big difference in readings between hot and if I just took it out of the garage and drove a couple of miles to the test place. 95 coupe/87k miles
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I'm sure your engine was sufficiently warm for it to pass - specs require that it be so and there's little need to drive the bejesus out of it if it's working right - which - yours may not be. Most HC and CO failures are because the ECM is delivering too much fuel. The other cause is the CAT. Can you scan it and get some BLM's? Makes it lot easier, but presuming it's adding fuel it doesn't need, then you look for anything that's letting extra air blow past the O2(s). That would include vacuum and exhaust (header) leaks and/or a faulty air pump circuit. Otherwise, if the scan shows that fuel delivery is honkydory, probably time for a new CAT. If you can get some numbers and post them, it would help.
Advanced
Joined: Apr 2006
Posts: 91
Likes: 0
From: Hotlanta Georgia
I have a 93 also, and failed emissions with similar numbers. While installing an oil cooler for my transmission I discovered that my air pump is seized up. Check yours to make sure it's running. I haven't been for a retest, and have not had any luck finding a rebuild kit for the pump, or a used one. The new baby is $200+ from what I have seen.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
I don't know how a seized pump would keep it from passing - The LT motors only use it at start up to help light off the O2(s) and CAT - It doesn't play a role once warmed up. Of course if you stay open loop, it isn't going to pass, but heated O2's should eventually get there. Usually if the pump circuit is the cause, it's because one of the header checkvalves is broken or the pump is continuing to run after it's up to temp. Either situation will cause the O2 to sense a lean condition and the ECM dumps in too much fuel.
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Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
Maybe - maybe not - if it doesn't, and the wiring is good (an open in the signal wire will generate the code) pull the check valve on the right header and make sure that air only goes through it in the direction of the header.
