emissions help
Thread Starter
1st Gear
Joined: Dec 2010
Posts: 1
Likes: 0
From: washington dc
emissions help
I have a 1981 corvette. I have added a 350/350 from the chevy dealer. I have added a aftermarket 350 trans and a 750 Holley Avenger. I cant pass Washington DC emissions. I have a cat and I take the carb off and put a smaller one on for the emission test as well as get the cat nice and hot. I have 2 mechanics. One said that I can"t pass emissions because I don't
have any of the original emission equipment. The other said that I can pass with just the cat converter as long as the carb is adjusted properly. does anyone have any advice for me> I need help to pass this emissions test.
have any of the original emission equipment. The other said that I can pass with just the cat converter as long as the carb is adjusted properly. does anyone have any advice for me> I need help to pass this emissions test.
Le Mans Master
Joined: Sep 2004
Posts: 5,116
Likes: 5
From: Livonia MI
Maybe see if your state allow's registering the car under antique/heritage status since it's over 25 year's old. Could probably skip the whole emission's process this way. Also, you mention cat(as in one). Assuming you now have true dual exhaust which mean's you need to run two. The modern smaller high flow cat's offer very little restriction, but need to keep an eye for to lean A/F carb setting's, or wont last long.
Burning Brakes
Joined: Aug 2006
Posts: 1,155
Likes: 0
From: San Diego California
Check the specific smog laws in your area. The DMV and/or smog test station should be able to direct you. Every state, and sometimes even local areas have different requirements. Its not unusual to have both visual inspections to ensure that all needed smog equipment is installed, as well as a tail pipe sniffer test for actual emissions. Do some research for your areas requirements.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
I'd find out first which one is right. Or, you could do the obvious and put the smog stuff back on your new engine.
Le Mans Master
Joined: Nov 1999
Posts: 5,768
Likes: 3
From: San Diego CA
I have a 1981 corvette. I have added a 350/350 from the chevy dealer. I have added a aftermarket 350 trans and a 750 Holley Avenger. I cant pass Washington DC emissions. I have a cat and I take the carb off and put a smaller one on for the emission test as well as get the cat nice and hot. I have 2 mechanics. One said that I can"t pass emissions because I don't have any of the original emission equipment. The other said that I can pass with just the cat converter as long as the carb is adjusted properly. does anyone have any advice for me> I need help to pass this emissions test.
have any of the original emission equipment. The other said that I can pass with just the cat converter as long as the carb is adjusted properly. does anyone have any advice for me> I need help to pass this emissions test.If you failed due to tailpipe emissions (usually conducted after a visual inspection - assuming a visual is part of your states test) then it boils down to getting all your equipment on and operating properly.
The Catalytic convertor does cover a multitude of sins and does the lions share of cleaning up your exhaust. Often a new Cat is all thats needed to pass the test (assuming you werent too far off).
You might post your failed test result, that could lead some of the more experienced members to help diagnose what issue you are having.
Safety Car
Joined: Mar 2007
Posts: 3,652
Likes: 49
From: Bridgewater nj
With the cold weather we're have here in the NE your cats may be cooling down also you may want too throw in a 210* thermostat to keep the heat up...
All this if you are passing the visual inspection
All this if you are passing the visual inspection
Instructor
Joined: Aug 2010
Posts: 233
Likes: 18
From: Monrovia Md
Ccc
The 1981 corvette has a CCC controlling mostly the Carb mixture and the timing advance. If you changed out the carb with a non CCC carb, Have you also replaced the Distributor? I am not sure, but can the timing advance being all screwed up cause you to fail emissions?
If it is a CCC Carb -- does the Check engine light come on -- if yes, what is the code. My 1981 had a check engine light on and would create horrible emmisions tests until I corrected it, mainly because the default setting is full rich.
If it is a CCC Carb -- does the Check engine light come on -- if yes, what is the code. My 1981 had a check engine light on and would create horrible emmisions tests until I corrected it, mainly because the default setting is full rich.
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Race Director
Joined: Jul 2004
Posts: 12,706
Likes: 329
From: Scottsdale Arizona
You've got all of the right questions above that you need to answer before solving the problem. First on the list is finding out why you failed and what needs to be there to pass. Without this information, you're just guessing. The most important difference is between a sniffer test and a real visual test. If both, you probably have a long way to go.
Once you know the regs and what you need to pass, the CCC will likely be your biggest hurdle. Since you've changed the carb you've removed the most important part of the 81 emissions system. A smaller carb won't make a difference. If any of your original computer system is still functional, the "Check Engine" light should be on all the time. In CA, that's an automatic Fail. Also mentioned above is that on 81's, the distributor is also computer controlled. I presume your's has been replaced along with the motor.
Last item is the motor itself. A 350/350 will certainly have more cam than your stock L81. That'll mean more emissions to clean up though it's certainly possible.
Agai, until you find out the local regs, we're just guessing.
The 1981 corvette has a CCC controlling mostly the Carb mixture and the timing advance. If you changed out the carb with a non CCC carb, Have you also replaced the Distributor? I am not sure, but can the timing advance being all screwed up cause you to fail emissions?
If it is a CCC Carb -- does the Check engine light come on -- if yes, what is the code. My 1981 had a check engine light on and would create horrible emmisions tests until I corrected it, mainly because the default setting is full rich.
If it is a CCC Carb -- does the Check engine light come on -- if yes, what is the code. My 1981 had a check engine light on and would create horrible emmisions tests until I corrected it, mainly because the default setting is full rich.
Last item is the motor itself. A 350/350 will certainly have more cam than your stock L81. That'll mean more emissions to clean up though it's certainly possible.
Agai, until you find out the local regs, we're just guessing.
Heel & Toe
Joined: May 2012
Posts: 22
Likes: 0
From: Los Angeles California
Hey, I'm in LA and scratching my head. This seems simple, I just don't want to spin my wheels. My new "old girl" (a "survivor") just failed smog. I cleaned up most of the trouble (HC, CO, O) with timing and proper gap on the plugs. At this point, my NO #s are 15mph= 1684 and 25mph= 1473 (both double the max). I have increasing vacuum at the EGR and, when connected directly to manifold vac, it slows the engine down. The cat looks older as well. Really hoping you can confirm my thoughts or get me going in the right direction. Thanks, in advance.
