Failed emissions.... Cats?
Le Mans Master
Joined: Dec 2000
Posts: 7,839
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From: San Diego, Ca
What the heck is a "header check valve"? 
It's only 1/25 times that it stumbles a bit when the AIR pump is running. I suppose that could be a result of a clogged cat- the air being pumped in has nowhere to go...
The muffler guy did use a heat probe to test it- it read hotter before the cat than after which he indicates is a sign of a bad cat. He clearly wasn't just trying to "sell me something" as he's the one that told me to go get it diagnosed before throwing money at it.
It's only 1/25 times that it stumbles a bit when the AIR pump is running. I suppose that could be a result of a clogged cat- the air being pumped in has nowhere to go...
The muffler guy did use a heat probe to test it- it read hotter before the cat than after which he indicates is a sign of a bad cat. He clearly wasn't just trying to "sell me something" as he's the one that told me to go get it diagnosed before throwing money at it.
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Team Owner
Joined: Apr 2001
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From: Overwhelmed as one would be, placed in my position.... DFW, TX
St. Jude Donor '05
Now THAT sounds reasonable! I think we're making progress here.
According to the link in my original post, high HC levels are the result of running too rich or too lean.
High CO is the result of running too rich.
My car has both issues, in addition to the NOX problem.
If the check valve is leaking, the engine would be running rich which would be the cause of my burned-out cat.
Car goes in tomorrow for testing- I'll make sure they check it.
According to the link in my original post, high HC levels are the result of running too rich or too lean.
High CO is the result of running too rich.
My car has both issues, in addition to the NOX problem.
If the check valve is leaking, the engine would be running rich which would be the cause of my burned-out cat.
Car goes in tomorrow for testing- I'll make sure they check it.
Cruising
Joined: Jul 2006
Posts: 11
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From: CA
Failed emissions ... cats
Last year my C4 (87) failed smog here in CA for the same thing. My pre-cats were non functional, gave me better performance and milage w/o them but had to buy a new head pipe w/ pre cats and the car passed smog better than factory w/ 100K miles on it. I had already installed new cat and mufflers previously except for the pre cats. I passed the smog test and now my milage suffers a little bit. I considered putting back on the old pipe but that too much work every two years for smogging the car.
As for cutting the pipes off would be good for performance but will never pass smog since I was told by GM they are part of burning off the gases. Good Luck!
Rich
As for cutting the pipes off would be good for performance but will never pass smog since I was told by GM they are part of burning off the gases. Good Luck!
Rich
Melting Slicks
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From: Palm Beach
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St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
Melting Slicks
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From: Palm Beach
I asked you what car you have because your profile is blank and you have a GS imitation for an avatar.
Last edited by MK 82; Mar 31, 2008 at 10:45 AM.
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St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
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St. Jude Donor '09-'10-'11-'12-'13-'14-'15-'16
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St. Jude Donor '03-'05-'06-'10-'11-'12
High NOx emissions are the result of high combustion chamber temps.
I fought the same battle and ultimately changed plugs to a colder range. Car passed with flying colors. I don't know for absolutes if that is the ultimate fix but it worked for me.
I fought the same battle and ultimately changed plugs to a colder range. Car passed with flying colors. I don't know for absolutes if that is the ultimate fix but it worked for me.
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From: Palm Beach
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Melting Slicks
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From: Palm Beach
You said I was wrong. And, since you know more than I.....I stated early on in my first explanation back to you about my experience with my '88 and what I was told by the dealer at that time. BTW, I gave you the year of the car in that post which you apparently did not read fully. I never claimed to know a whole lot about the system other than what I've been told and have gathered in the years I've owned Vettes. I'm not saying that you have said anything "wrong". I am saying that when asked a direct question you have danced around and been totally evasive. So, I'll ask you one more time. Why did the dash light come on when it did (days before hard starting and noticeable loss of power), read a code #13 for the dealer that led to being diagnosed as a bad cat?
Le Mans Master
Joined: Dec 2000
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From: San Diego, Ca
Go out and look at your headers (assuming they're stock) - modern cats don't need air - and if they did, say like the L98's, there would be a direct connection. Now what's passing through the headers eventually reaches the CAT but your '94 has an electric pump to assist those heated O2's - so do a lot of cars. The sooner you get to Closed Loop the better the Emissions.
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From: Overwhelmed as one would be, placed in my position.... DFW, TX
St. Jude Donor '05
Oh dear... Look what I started. 
Took the car to GM, they came back indicating that the ONLY thing that appears to be faulty are the cats. They connected it to some scan machine and indicated that everything was clean except code 420 which they said means the cats are shot. The SM told me that they checked the EGR valve and it was fine. When I indicated that cats generally do "go bad", he said that the car really did test out just fine.
Ooookay...
So I went to the muffler place to have new cats welded in. when the cut them off, I took a gander. One of them seemed to be in poor condition, but I could see daylight through the honecombs. The other one... about have the catalyst was gone... Yeah, definately toast.
It goes back for testing this evening- we'll see if it passes. If it doesn't pass with flying colors, I'm going to pay the SM at the dealer a nasty visit.
Took the car to GM, they came back indicating that the ONLY thing that appears to be faulty are the cats. They connected it to some scan machine and indicated that everything was clean except code 420 which they said means the cats are shot. The SM told me that they checked the EGR valve and it was fine. When I indicated that cats generally do "go bad", he said that the car really did test out just fine.
Ooookay...
So I went to the muffler place to have new cats welded in. when the cut them off, I took a gander. One of them seemed to be in poor condition, but I could see daylight through the honecombs. The other one... about have the catalyst was gone... Yeah, definately toast.
It goes back for testing this evening- we'll see if it passes. If it doesn't pass with flying colors, I'm going to pay the SM at the dealer a nasty visit.
Melting Slicks
Joined: Feb 2008
Posts: 3,286
Likes: 6
From: Palm Beach
Go out and look at your headers (assuming they're stock) - modern cats don't need air - and if they did, say like the L98's, there would be a direct connection. Now what's passing through the headers eventually reaches the CAT but your '94 has an electric pump to assist those heated O2's - so do a lot of cars. The sooner you get to Closed Loop the better the Emissions.