'92 LT-1 Fails Emission Test
Thread Starter
4th Gear
Joined: Dec 2001
Posts: 4
Likes: 0
From: Dallas TX
'92 LT-1 Fails Emission Test
Posting this for a friend ... all suggestions are appreciated.
The vehicle is an 1992 LT-1, 350cid, auto Xmission with 52K miles, and it fails the annual exhaust emissions test. The car appears to be running normally and has no other (engine related) issues. The car gets good fuel mileage (20-24mpg if memory serves). The plugs, plug wires, fuel filter, air filter and PVC valve have all been replaced, but no improvement.
The tests indicate the HC content @ 300ppm and CO @ 2%, which is apparently over the limits in Dallas.
Thanks in advance for your help!
Howard Duncel
hduncel@anonymous.to
The vehicle is an 1992 LT-1, 350cid, auto Xmission with 52K miles, and it fails the annual exhaust emissions test. The car appears to be running normally and has no other (engine related) issues. The car gets good fuel mileage (20-24mpg if memory serves). The plugs, plug wires, fuel filter, air filter and PVC valve have all been replaced, but no improvement.
The tests indicate the HC content @ 300ppm and CO @ 2%, which is apparently over the limits in Dallas.
Thanks in advance for your help!
Howard Duncel
hduncel@anonymous.to
Team Owner
Joined: Sep 2001
Posts: 62,160
Likes: 1,733
From: Athens AL
C7 of the Year - Unmodified Finalist 2021
C4 of Year Finalist (performance mods) 2019
Re: '92 LT-1 Fails Emission Test (Goody)
yeah we need to know if its modified, a stock car shouldnt fail emissions unless something is really wrong.
Team Owner
Joined: Aug 2000
Posts: 40,156
Likes: 45
From: San Pedro CA
Re: '92 LT-1 Fails Emission Test (hduncel)
sounds like it is running a touch rich... or the cats are bad... or both...
There is also a chance their machine is out of calibration, too... I would get a bottle of "Smog Check", or the equivalant additive... add it to about 1/2 a tank of gas... it will pass!!!
There is also a chance their machine is out of calibration, too... I would get a bottle of "Smog Check", or the equivalant additive... add it to about 1/2 a tank of gas... it will pass!!!
Drifting
Joined: Mar 2000
Posts: 1,630
Likes: 1
From: Woodstock GA
Re: '92 LT-1 Fails Emission Test (hduncel)
If the cats are still there I would suspect a possible problem with one or both O2 sensors, even with engine mods if everything is still there and working it should pass, when they don't and the car seems to run good I find Os sensors to be the most likely problem I would also use only A/C Delco sensors I find aftermarket sensors to be slightly different calabration and can make cars fail. If you know someone with a Tech-1 and MAS storage cartrage they can run an O2 sensor test and tell you if you have problems you can also use a scope or diacom were you can graph the sensor that is also a good way to tell if they are any good but if they are original it would be a good idea to replace them anyway. Again this is all dependent on the fact that there are cats on the car and working.
David Fulcher
David Fulcher
Team Owner
Joined: Oct 2000
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St. Jude Donor '03-'04
Cruise-In 1-2-3-4-5 Veteran
Re: '92 LT-1 Fails Emission Test (David-F)
O2 sensors, maybe.
Might be a good time to upgrade to a new Bosch heated sensor.
Also...before you test, go for a ten-mile drive to make sure that your engine and your cats are 100% warmed up. Heaviest pollution happens at startup and cold driving, because the cats have to get hot to work.
My '93 passes like a LEV here in Nashville.
Might be a good time to upgrade to a new Bosch heated sensor.
Also...before you test, go for a ten-mile drive to make sure that your engine and your cats are 100% warmed up. Heaviest pollution happens at startup and cold driving, because the cats have to get hot to work.
My '93 passes like a LEV here in Nashville.
Instructor
Joined: Oct 1999
Posts: 152
Likes: 0
From: Tewksbury MA
Re: '92 LT-1 Fails Emission Test (hduncel)
I assume that the engine had been running for at least a half hour and was at fan turn on temperature. Also, the engine oil should have been very recently changed. Those things are SOP for passing emissions testing with a sound engine.
I agree that the O2 sensors are an easy fix, and should be the first repair. New sensors after 50K miles are not a bad idea anyway.
There are products out there that loosen up hydrocarbons and clean them up. Some of them work as oil additives and some work as fuel additives. They are worth a shot, and are available at many auto supply stores. On example is a product called "Guaranteed to pass." Also, to get right into the motor and remove hydrocarbons, you can pull the throttle body and clean it with brake cleaner, or other products. That will help some. And there are products that get sucked into the motor by vacuum, and loosen the stuff inside.
Check out Run Rite products @ http://www.run-rite.com/welcome.htm I have used their stuff and it does work, although it is not cheap.
Also, in Massachusetts there are registry authorized emissions "repair" stations. If you have those in Texas, it might be worth while talking to them. If the motor is original and right, and the cats are not too bad, it should pass easily.
I agree that the O2 sensors are an easy fix, and should be the first repair. New sensors after 50K miles are not a bad idea anyway.
There are products out there that loosen up hydrocarbons and clean them up. Some of them work as oil additives and some work as fuel additives. They are worth a shot, and are available at many auto supply stores. On example is a product called "Guaranteed to pass." Also, to get right into the motor and remove hydrocarbons, you can pull the throttle body and clean it with brake cleaner, or other products. That will help some. And there are products that get sucked into the motor by vacuum, and loosen the stuff inside.
Check out Run Rite products @ http://www.run-rite.com/welcome.htm I have used their stuff and it does work, although it is not cheap.
Also, in Massachusetts there are registry authorized emissions "repair" stations. If you have those in Texas, it might be worth while talking to them. If the motor is original and right, and the cats are not too bad, it should pass easily.
Pro
Joined: Dec 2001
Posts: 715
Likes: 0
From: NYC NY
Re: '92 LT-1 Fails Emission Test (hduncel)
I'm with bogus. Sounds like it is running rich. Mine did the same thing and it was because of too much fuel pressure. If you have an adjustable fuel pressure reg. it's real easy to over do it. Just something you might want to check.
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Thread Starter
4th Gear
Joined: Dec 2001
Posts: 4
Likes: 0
From: Dallas TX
Re: '92 LT-1 Fails Emission Test (hduncel)
Thanks all for the help and suggestions. The car is stock, the engine oil was recently changed, and as far as the engine being warm at the time of testing, well ... I don't have that info.
My friend purchased the car used, and this is the first time it's been inspected while he's owned it (less than 6 months), so it's possible to have had the problem all along.
As far as the catalytic convertors go, again to the best of knowledge they are in place, but that doesn't tell us if they are working. I suggested he have the emissions test run above the cats to see if they were doing anything at all. I'll also suggest he replace the oxygen sensors.
Again, thanks for all the help and ideas!!!
My friend purchased the car used, and this is the first time it's been inspected while he's owned it (less than 6 months), so it's possible to have had the problem all along.
As far as the catalytic convertors go, again to the best of knowledge they are in place, but that doesn't tell us if they are working. I suggested he have the emissions test run above the cats to see if they were doing anything at all. I'll also suggest he replace the oxygen sensors.
Again, thanks for all the help and ideas!!!
Safety Car
Joined: Dec 2000
Posts: 3,767
Likes: 5
From: Jacksonville Fl
Re: '92 LT-1 Fails Emission Test (hduncel)
First is to do general maintenance. Change oil and spark plugs. CLean the throttle body of gunk ( removing it and cleaning it is the best way ). Change the air filter. Changing the O2 sensors will help, but may not be necessary.
I usually increase the minumum air flow by adjusting the throttle blade idle screw slightly, then back off the TPS sensor setting a little. This usually make any car pass inspection.
Make sure the car is driven enough to be hot before testing.
I usually increase the minumum air flow by adjusting the throttle blade idle screw slightly, then back off the TPS sensor setting a little. This usually make any car pass inspection.
Make sure the car is driven enough to be hot before testing.
Safety Car
Joined: Mar 2000
Posts: 3,620
Likes: 2
From: Hillsboro OR
Re: '92 LT-1 Fails Emission Test (hduncel)
I go with David-Fs advice. I can't remember exactly but I know he works for a GM dealer and see's problem like you have all the time. Check the cats first, then the O2s.