81 failed Emissions test
Race Director
Joined: Sep 1999
Posts: 11,360
Likes: 382
From: Plano TX
Re: 81 failed Emissions test (Gator81)
Gator: I agree that replacing the cat shouldn't fix a NOx problems per se. However, there is one scenario where a bad cat can cause high NOx. If the cat is partially plugged, the increased back pressure will increase cylinder temps and can cause high NOx. Since he plans on replacing the cat anyways (and he should if it's the original one), it might just solve the problem. Of course, I wouldn't go for a re-test without checking (retarding) timing and making sure the EGR works.
What amazes me is that he managed over 2000 ppm NOx. Even without EGR it hard to get that much. Makes me think the timing is advanced.
What amazes me is that he managed over 2000 ppm NOx. Even without EGR it hard to get that much. Makes me think the timing is advanced.
6th Gear
Joined: Mar 2002
Posts: 6
Likes: 0
From: Marietta Georgia
Re: 81 failed Emissions test (ksems)
NOX is oxides of nitrogen ie:NO1,NO2,NO3 ect. On a SBC it is always an EGR problem.The exauast gas is an inert gas that will not burn,it it reintroduced into the intake to cool combustion temps. To test the EGR itself,with the engine running put your fingers under the valveand pull it up this should cause a drop in RPM's if it drops the EGR is good if not the valve is bad or the EGR port is stoped up.Next check for proper vacume pull off the vac. line with engine running @ low RPM there must be no vacume,then rev it up and there will be vacume this is called ported vacume.If there is no vacume repair vac. line
Good luck Mark
ASE Master Tech
:yesnod:
Good luck Mark
ASE Master Tech
:yesnod:
Thread Starter
Pro
Joined: Aug 2000
Posts: 573
Likes: 0
From: Alpharetta GA
Re: 81 failed Emissions test (SUPERTECH)
supertech -
I think the EGR is good , Ill check it this weekend though, or tomorrow, I have the day off so.....
got to figure out the problem.
Thanks
Kevin
I think the EGR is good , Ill check it this weekend though, or tomorrow, I have the day off so.....
got to figure out the problem.
Thanks
Kevin
Thread Starter
Pro
Joined: Aug 2000
Posts: 573
Likes: 0
From: Alpharetta GA
Re: 81 failed Emissions test (ksems)
here is something I forgot. The guy testing it said that he turned on the heater in the car to see
if that would help and that it actually made it worse...
whats up with that?
if that would help and that it actually made it worse...
whats up with that?
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Pro
Joined: Jan 2000
Posts: 569
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From: SLC, UT USA
Re: 81 failed Emissions test (ksems)
Last spring had the same probelem on my '81. No air punp & no cat. Had it tested on a hot afternoon and the testing station did not switch on the large fans to provide air flow to the radiator, plus they let it sit and idle for a while.
So next moring while temps were still cooler, drove back to testing station. Did not let it sit and idle, opened hood while I waited, and insisted they switch on the cooling fans in the shop.
Worked like a charm and passed with very low emissions.
So next moring while temps were still cooler, drove back to testing station. Did not let it sit and idle, opened hood while I waited, and insisted they switch on the cooling fans in the shop.
Worked like a charm and passed with very low emissions.
Racer
Joined: Nov 2001
Posts: 251
Likes: 0
From: Lake Hughes CA
Re: 81 failed Emissions test (ksems)
I would change the thermostat back to the 195 factory along with turning back the timing. The reason I would change the stat back is you do have computer/carb vette (as I do). The egr is controlled by the computer and I am not sure at what temp the system goes into closed loop operation. The computer also control your mixture with your electronic Q-jet.
good luck
good luck
Racer
Joined: Jul 2001
Posts: 429
Likes: 0
From: Norfolk Va VA
Re: 81 failed Emissions test (zwede)
Check the rest of your EGR system. Maybe the Valve itself is good.
Racer
Joined: Jul 2001
Posts: 429
Likes: 0
From: Norfolk Va VA
Re: 81 failed Emissions test (gerry c)
I would change the thermostat back to the 195 factory along with turning back the timing. The reason I would change the stat back is you do have computer/carb vette (as I do). The egr is controlled by the computer and I am not sure at what temp the system goes into closed loop operation. The computer also control your mixture with your electronic Q-jet.
good luck
good luck
Le Mans Master
Joined: Apr 1999
Posts: 6,134
Likes: 46
From: Raleigh North Carolina
Re: 81 failed Emissions test (ksems)
"or the EGR port is stoped up"
This is very common, constantly overlooked until tons of money has been spent replacing things that weren't broken in the first place.
I have cleaned out many EGR passages (by soaking & media blasting) that were causing emissions test failure.
If it doesn't pass after you replace everything, check out the EGR passage.... see if it is clear.
Just a "heads up".
This is very common, constantly overlooked until tons of money has been spent replacing things that weren't broken in the first place.
I have cleaned out many EGR passages (by soaking & media blasting) that were causing emissions test failure.
If it doesn't pass after you replace everything, check out the EGR passage.... see if it is clear.
Just a "heads up".
Intermediate
Joined: Mar 2002
Posts: 49
Likes: 0
From: Hillard Ohio
Re: 81 failed Emissions test (Tom454)
It's not the converter. I don't think that GM was using 3-way cats in 1981.
Make sure your EGR is WORKING. If you apply full vacuum to the EGR valve while the engine is idling the engine should stall. The EGR valve should also hold vacuum when you apply vacuum with a vacuum pump.
If the EGR valve checks out fine then either your timing is advanced too far at idle or you are running too lean.
Good luck!
rocky
Make sure your EGR is WORKING. If you apply full vacuum to the EGR valve while the engine is idling the engine should stall. The EGR valve should also hold vacuum when you apply vacuum with a vacuum pump.
If the EGR valve checks out fine then either your timing is advanced too far at idle or you are running too lean.
Good luck!
rocky
Thread Starter
Pro
Joined: Aug 2000
Posts: 573
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From: Alpharetta GA
Re: 81 failed Emissions test (gerry c)
I reinstalled a 195 thermostat.....and checked the timing
the timing was at 6 degress BTC.....right where the sticker says it should be...
I havent retested because the only thing Ive done is the thermostat..
should I go get it retested?
Also , I pulled up on the EGRand the engine stalled...so i guess the valve is okay.
now what?.....
Thanks
Kevin
the timing was at 6 degress BTC.....right where the sticker says it should be...
I havent retested because the only thing Ive done is the thermostat..
should I go get it retested?
Also , I pulled up on the EGRand the engine stalled...so i guess the valve is okay.
now what?.....
Thanks
Kevin
Racer
Joined: Nov 2001
Posts: 251
Likes: 0
From: Lake Hughes CA
Re: 81 failed Emissions test (ksems)
I would probably kick the timing back a couple more degrees to like four or so. That will help the NOX a little more. I would also change plugs since you are in there and they are cheap. Setting the timing back may cause some of your other numbers to go up. Change the oil and filter also.
Just a couple hints I've gained from living with the pollution controls in the Peoples Republic of Kalifornia.
You can always bump the advance back up after you pass smog.
The 195 stat should help a lot. The computer does control the carb, egr, and timing on your car.
Good Luck and happy :smash:
Just a couple hints I've gained from living with the pollution controls in the Peoples Republic of Kalifornia.
You can always bump the advance back up after you pass smog.
The 195 stat should help a lot. The computer does control the carb, egr, and timing on your car.
Good Luck and happy :smash:
Burning Brakes
Joined: Feb 2001
Posts: 866
Likes: 1
From: Peabody,MA,USA
Re: 81 failed Emissions test (gerry c)
Retard the timing a lot and then reset it after you pass the test. You can retard the timing so much that it wont complete the burn in the cylinder and will keep on burning as it goes out the exhaust valve. This will give you low cylinder pressure and temp and low NOx.
Thread Starter
Pro
Joined: Aug 2000
Posts: 573
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From: Alpharetta GA
Re: 81 failed Emissions test (73Ken73)
allright - setting the timing back is worth a try....Ill set it to 4.
Will my car run at 4 without upping the idle or mixture ??
From what I under stand the MIXTURE is NOT something that I should mess with - computer doesnt like that....:mad:
is my idle speed on the drivers side front of the carb?
for those that asked - I have already replaced the plugs , wires.....and oil/filter.
thanks for the advice though......:)
I just want this damn thing to pass...
Kevin
[Modified by ksems, 7:52 AM 3/17/2002]
Will my car run at 4 without upping the idle or mixture ??
From what I under stand the MIXTURE is NOT something that I should mess with - computer doesnt like that....:mad:
is my idle speed on the drivers side front of the carb?
for those that asked - I have already replaced the plugs , wires.....and oil/filter.
thanks for the advice though......:)
I just want this damn thing to pass...
Kevin
[Modified by ksems, 7:52 AM 3/17/2002]