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Old 03-21-2003, 12:53 PM   #1
GKK
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Failed emmisions high HC/NOX

A couple of weeks before the test I changed the oil, cap & rotor, installed new A/C delco spark plugs, have Taylor Spiro Pro plug wires changed the O2 sensor about a year ago and installed a Random Technology high flow Cat about two years ago. The only thing I didn't change was the EGR valve. Could this be why I failed on both the HC and NOX?
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Old 03-21-2003, 05:36 PM   #2
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I took my car to my mechanic and he said that according to his diagnostic equipment the engine should pass but, later found that his diagnostic equipment must have been out of calibration because he took my car back to the smog station and it failed again there. My mechanic thinks the catalytic converter is not working right. I hope I don't have to get another catalytic converter since I just bought the Random Technology Cat a year ago.

Last edited by GKK; 03-22-2003 at 12:18 PM.
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Old 03-22-2003, 05:51 AM   #3
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maybe your friend's was right and the shop's was off???
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Old 03-22-2003, 12:24 PM   #4
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Last night after reading all the past posts on emissions, I came to the conclusion that the engine must be running lean due to both the high HC and NOX. I adjusted the fuel pressure to 14psi at idle and the engine ran noticeably smoother. The fuel pressure was set to 12psi before. I'm getting it re-inspected on monday, I hope it passes.
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Old 03-22-2003, 12:44 PM   #5
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High HC suggests rich, not lean. It could also mean the cat isn't working.
NOx suggests too advanced spark timing, EGR not working, or the cat is bad...

I'm curious to see if it will pass with higher fuel pressure. It may bring the NOx down, but HC will still fail.
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Old 03-22-2003, 04:43 PM   #6
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GKK-
Did you re-connect the AIR tube going into your cat if you had one? If not, the cat may not be able to burn all hydros efficiently.
I agree with Kevm on his call of high HC being too rich, not lean.

Am I reading your test slip right when it says you pass at 25 mph, but not at 15?
Are you buring any oil? How many miles are on it?

S-D

Also- if high mileage, may need to test/clean your EGR valve (in response to NOx values).
S-D
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Old 03-22-2003, 11:17 PM   #7
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Quote:
Did you re-connect the AIR tube going into your cat if you had one? ).
Yes, I have the AIR tube connected to the Random Technology Cat. My "91" LO3 engine has 94,000 miles on it and is very well maintained. Today I installed a new EGR and PCV valve so we'll see on monday if it will pass.

Also, in all the posts I've been reading about emissions, most say that high HC is due to an incomplete burn in the combustion chamber usually from a bad ignition system, low compression or worn valve seals, vacuum leaks or a lean misfire causing the mixture to not burn completely which would send some unburnt fuel through the exhaust.

High NOX is usually caused from high combustion temperatures which a bad EGR could contribute to.

This is just what I've read so far but, thanks for your opinions. I'll search some more to make sure I haven't misread anything.

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Old 03-24-2003, 02:21 PM   #8
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I had my car re-tested today and it still failed NOX. After raising the fuel pressure to 14psi the HC came down a lot but the NOX increased by a 100ppm. I have a feeling that my Random Technology Cat isn't doing it's job.
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Old 03-24-2003, 03:21 PM   #9
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I'm going to speculate that your HC came down not because of the fuel pressure increase, but because conditions were different. I.e. you drove it longer before getting tested, you idled less before the test, the engine was hotter, etc.

Anyway, try a new EGR and solenoid before dealing with the cat...but the cat could very well be the problem.

Good luck
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Old 03-24-2003, 06:29 PM   #10
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I too failed emissions with my 89 model...
They said I was practically dumping raw fuel out of my exhaust. I went in before tuneup and I do notice a slightly rough idle at times. I have not gone back yet but I did cap rotor wires and pcv valve so far. She feels better. Idle is still slightly rough so I am going to try plugs too. But they said highest I could be was .85 I tested at 1.018.

Think what I have done so far will get me there? If not will the plugs do it? Also I have heard of running some alcohol in your tank to help you pass... where would I get this? How much would I need etc? Also since I guess I am running rich would cutting down fuel pressure do it and if I do that how would I go about it? This is my first GM so I am unsure of how to do that...

Also I am in missouri and our st.louis emissions stations are suppose to take our vehicles to a max of 58mph. Well I had a good shot of the tach in my car when they did the testing and he was running 3 grand in OD! I run 2000 rpms at 70mph!!! Also they peeled out did not apologize for it. Then popped my hood without permission.. then they could not figure out how to open it..... GGRRR... then pointed out my open element as the cause of the problem and suggested I replace it with stock ****...

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Old 03-25-2003, 02:16 PM   #11
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sounds like a cat for sure. I had the same problem... after running a set of 3" catco high flow cats I failed with NOX. Put stock cat back on and got another since I ran true dual and almost passed... i had a hookup at the emission test station... he still tested my car... i would have passed... but i removed my rear brakes at the time so they couldnt stop it on the treadmill and his boss wouldnt let it go...
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Old 03-25-2003, 06:19 PM   #12
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My car recently failed emissions as well. I just got a capacitive discharge multi-spark ignition box. Perhaps that will help burn more of the fuel?
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Old 03-25-2003, 07:52 PM   #13
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the "capacitive discharge multi spark whatever" will not burn more fuel unless u have more air to burn it with., that just prevents misfires
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Old 03-25-2003, 11:28 PM   #14
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I have a solution that involves the mofia
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Old 03-26-2003, 11:27 AM   #15
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I think I found the problem. I just noticed that my fans were turning on and off at various temperatures (not the normal 200* on 185* off) so I checked and replaced the fan relay and also, think my Jet-Fan Switch is failing causing the combustion chamber temps to be hotter than usual at idle causing the high NOX readings. I just ordered a Hypertech fan switch and hope that solves the problem.
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Old 03-26-2003, 11:27 AM
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