help!

motroman

New Member
Joined
Jul 3, 2003
After a week and a half at a "gross polluter" Calif. smog station, over a grand in repairs, my new 86, totally stock, GN finally passed California smog.

The mechanic still thinks something is wrong and the vehicle will fail again, but, short of replacing everything, he doesn't know what.

It's my nature to solve a problem sooner rather than later, so now that I have two years before the next smog test, I want your opinion about what is causing the failure.

First the facts, the first failed test

Co2 o2 HC CO

12.70 0.00 679 0.55 - idle

13.90 0.00 25 0.23 - 2500 rpm

the HC idle figures sent the car to the "gross polluter" station. Max in Calif. for my car is 120.

after checking plug wires, changing plugs and filters, replacing o2 sensor, replacing egr sensor, cleaning injectors, replacing the cat, checking the stock ecm for codes, the car passed, ...barely

Co2 o2 HC CO
13.0 2.3 65 0.31 - idle
14.1 0.8 19 0.09 - 2500 rpm

The car is running rich at idle but I don't know why. So, short of replacing all sensors, injectors, and the ecm,..what should I do?

Thanks for your help.
 
Says you replaced EGR sensor, is that the EGR valve itself? Did you install an aftermarket or factory unit? If you installed a aftermarket, is it the type with flow restriction washers? I'm not a supporter of aftermarket EGR valves. I like the factory stuff if I can get it. It is quite possible that the EGR valve is leaking at the diaphram.
 
It was a factory egr sensor and the mechanic checked the valve and said it was okay. He also did a vacuum leak test of the entire system(smoke test?) and it was also okay.
 
Originally posted by motroman
After a week and a half at a "gross polluter" Calif. smog station, over a grand in repairs, my new 86, totally stock, GN finally passed California smog.

<snip>

Co2 o2 HC CO
13.0 2.3 65 0.31 - idle
14.1 0.8 19 0.09 - 2500 rpm

The car is running rich at idle but I don't know why. So, short of replacing all sensors, injectors, and the ecm,..what should I do?

Thanks for your help.

Looking at the Low Co2, and the high O2 (at idle..sorry), I suspect a cracked exh manifold, or something intruducing air that the engine doesnt really need. The O2 sensor is seeing it and telling the ECM to add some fuel.

You may try purposly sending the car rich, or using some GM tope engine cleaner (to get the car to smoke) to see if you can see the exh leak.

The leak isnt large enough off idle to cause the ECM to make an adjustment. Which is evidenced by the 2500 rpm Co2 at 14+ (good complete combustion) and O2 under 1% meaning either the engine is burning it all up, or the cat is using it as an oxidizer, either way, get the idle numkbers to look like the 2500 rpm numbers and you'll be golden.

BTW, its a good possibility that if the car was in such a bad state of tune that it blew almost 700ppm, and you drove it like thbis for awhile, that the catalytic converter is dying/dead as well.

If you have access to a 5 gas analyzer, I can give you a pretty good procedure for testing a cat. Not just the in/out kinda efficiency, but its ability to store and use oxygen

Speaking of cats, today I was humbled by a Jeep Grand Cherokee that failed CO emissions. .59% CO no matter what I did, including fooling the ECM with vacuum leaks etc. Come to find it had a bad cat. The last thing I would have ever thought being used PURPOSLY to lower Co as well as HC/NOx (Jeeps 4.0'[s) have no EGR) As stupid as it may sound, I never realized the importance of a cat in reducing CO as well as HC/NOx

I know, I know, you all knew this already. Just sharing anyway :)
 
Thanks for the advice everyone. The car was tuned shortly before the test at the same shop that did the smog repairs. However, as you mentioned, it could have eaten up the cat way before the tuneup and that wouldn't be discovered until the day of reckoning.

It now has a new GM cat, so we'll see it it eats up that one too. I like the idea of checking the exhaust manifold. I'll do that this weekend. Thanks again everyone for the great advice.
 
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