Emissions Problems with 1981 getting UGLY
Thread Starter
Pro
Joined: Jan 2000
Posts: 569
Likes: 0
From: SLC, UT USA
Emissions Problems with 1981 getting UGLY
This is getting ugly!!
Plates expired end of May and still can't get it to pass.
Originally, the carb had some major problems and my CO was something like 28 times the max allowable. Rebuilt the carb and the next test showed 25 mph CO % as 2.49, allowable is 2.34. Figure I was almost there and would teak a few things to get it to pass the next emission test
Replaced the PCV, changed the oil, cleaned, and reoiled the K&N air filter. Next test shows higher at 2.70??
Next, followed in-laws advice and put in a bunch of fuel line anti freeze that has meth alcohol. Now CO tested even higher at 2.90!?!% So, I drove out most of that fuel, about ¼ of a tank, and re-filled the tank.
Over this last weekend, I installed new Bosch platinum plugs and replaced a burned plug wire. Took it in again to have another test.
When the Vette was being driven onto the rollers I knew it wouldn’t pass as the exhaust look kind of dark. CO now at 3.35%
The car has always passed the tail pipe test without even being close to the max, now seems like everything I do, except the carb rebuild, makes it run worse.
What should I do next?
Plates expired end of May and still can't get it to pass.
Originally, the carb had some major problems and my CO was something like 28 times the max allowable. Rebuilt the carb and the next test showed 25 mph CO % as 2.49, allowable is 2.34. Figure I was almost there and would teak a few things to get it to pass the next emission test
Replaced the PCV, changed the oil, cleaned, and reoiled the K&N air filter. Next test shows higher at 2.70??
Next, followed in-laws advice and put in a bunch of fuel line anti freeze that has meth alcohol. Now CO tested even higher at 2.90!?!% So, I drove out most of that fuel, about ¼ of a tank, and re-filled the tank.
Over this last weekend, I installed new Bosch platinum plugs and replaced a burned plug wire. Took it in again to have another test.
When the Vette was being driven onto the rollers I knew it wouldn’t pass as the exhaust look kind of dark. CO now at 3.35%
The car has always passed the tail pipe test without even being close to the max, now seems like everything I do, except the carb rebuild, makes it run worse.
What should I do next?
Advanced
Joined: May 2002
Posts: 50
Likes: 0
From: Brentwood TN
Re: Emissions Problems with 1981 getting UGLY (dsagers)
I know this is not much help, but I had a similar problem with my 79 L-82. I did the normal tune-up stuff (Plugs, wires etc) and changed all my vacuum hoses. I also had a hole in my Muffler Y-Pipe so I purchased a new kit from Ecklers and took it to a local muffler shop. While I was there they told me my Catalytic Converter was shot, so I had that changed as well. I told the mechanic about the Emissions failure and he put it on his tester. It was still showing the CO was too high, so he made two simple adjustments (He said it was the fuel-mixture) on the front on my Rochester Carburetor and it fell within limits. I took my car in the next day for a retest and it passed with flying colors. The nice thing about it is he didn’t even charge me for the adjustment. I am not sure which Carburetor you have, but I purchased a book on Rochester Carburetors and if you have this brand, I will be glad to send you any information that I can. Good luck!
Melting Slicks
Joined: Jun 2001
Posts: 2,340
Likes: 2
From: Moro IL
Re: Emissions Problems with 1981 getting UGLY (dsagers)
If it's an 81, then you have the E4ME Rochester. Not a whole lot of adjustment can be made on it at idle easily. Your CO is high meaning your rich for some reason. If you have a scan tool available I'd be curious to see what your O2 sensor is doing. Your O2 sensor is the only sensor in that system that can do any sort of measurement of your A/F ratio, actually it doesn't measure your A/F ratio directly but does it off of the oxygen content in the exhaust. You can read O2 sensor reading with a Volt meter set on a 2v scale. Your readings once warmed up should be between .01 and .99v and should switch back and forth fairly rapidly between high and low voltages, if it's stuck low or high you probably have a bad O2 sensor, either that or some sort of fuel related problem. I normally recommend not using platinum plugs on these engines, I can normally get better emmision readings with conventional plugs over platinum. By the way how are the HC's. EGR problems can also cause high CO, so make sure your EGR valve isn't stuck in an open position.
:cheers:
Pat Kunz
:cheers:
Pat Kunz
Le Mans Master
Joined: Mar 2002
Posts: 7,056
Likes: 40
From: Life is Messy, Bring a mop
Re: Emissions Problems with 1981 getting UGLY (dsagers)
73 LS4 is pretty much spot on. You can adjust the idle mixture on your rochester and this should be done (especially after a rebuild). It's best to do with a calibrated testor but can be done well enough to pass with a vacum gauge.
Your screws may be under aluminum plugs on the front of the carb. The plugs will have to be removed to adjust the carb (should have removed them during the rebuild to replace the "O" rings on the mixture screws).
Follow the instructions in a haynes (or chiltons) manual for any earlier model running a Q'jet. (i.e. lean to a stumble and then richen for max vacum).
Pretty easy really, just follow the book. The rochestor book mentioned is a big help.
Don't let anyone talk you into swapping out your carb. Rochestors are great carbs once you figure them out.
Good luck!
Your screws may be under aluminum plugs on the front of the carb. The plugs will have to be removed to adjust the carb (should have removed them during the rebuild to replace the "O" rings on the mixture screws).
Follow the instructions in a haynes (or chiltons) manual for any earlier model running a Q'jet. (i.e. lean to a stumble and then richen for max vacum).
Pretty easy really, just follow the book. The rochestor book mentioned is a big help.
Don't let anyone talk you into swapping out your carb. Rochestors are great carbs once you figure them out.
Good luck!
Le Mans Master
Joined: Mar 1999
Posts: 6,744
Likes: 1
From: delmont pa
Cruise-In I Veteran
Cruise-In II Veteran
Re: Emissions Problems with 1981 getting UGLY (dsagers)
do you have the special tools to set the rich/lean mixture stops for the metering rods,if not this could be your problem. :chevy
Safety Car
Joined: May 2001
Posts: 3,758
Likes: 3
From: Surrey
Re: Emissions Problems with 1981 getting UGLY (clem zahrobsky)
On the E4ME there is also the TPS which could be playing up & fooling the computer.
As well as the idle mixture screws at the front of the carb there is the Idle Air Bleed valve which is in the top of the carb (at the highest point) and should be under a metal plate (to stop us maniacs from fiddling with the settings). The IAB valve is used in conjuction with the mixture screws to set the idle mixture.
Another possibility is a vacuum leak. If the manifold vacuum is low, I think the computer decides that it's due to acceleration & richens the mixture up.
Just a couple of thoughts, hope they help,
:cheers:
As well as the idle mixture screws at the front of the carb there is the Idle Air Bleed valve which is in the top of the carb (at the highest point) and should be under a metal plate (to stop us maniacs from fiddling with the settings). The IAB valve is used in conjuction with the mixture screws to set the idle mixture.
Another possibility is a vacuum leak. If the manifold vacuum is low, I think the computer decides that it's due to acceleration & richens the mixture up.
Just a couple of thoughts, hope they help,
:cheers:
Burning Brakes
Joined: Aug 1999
Posts: 774
Likes: 0
From: Palatine IL
Re: Emissions Problems with 1981 getting UGLY (dsagers)
Do what the above posts say. Here is what I do to get my 1980, modified, no cat Vette to pass the sniffer test. My 1980 has no computer so in IL it does not have to go on the dyno if it passes the sniffer. These "creative tuning" techniques may or may not work for your Vette but they work for mine. They are in order of what I think makes the most difference:
* make sure EGR valve working correctly
* set idle to 1000-1200 rpm (1300 max test setting in IL)
* set timing to 2-4 degrees BTC @ 700 RPM
* set carb idle mixture screws adjusted slightly lean (1/4 turn in from normal performance setting)
* drive 30 minutes to warm engine and do not shut off in waiting line
* new oil and filter
* add Heat brand water remover (meth alcohol) to 10 gallons of gas
* new air filter or just remove it for test (max fresh air)
* new PCV valve or just remove it from valve cover (max fresh air)
Good luck. You didn't get these from me. :blueangel:
* make sure EGR valve working correctly
* set idle to 1000-1200 rpm (1300 max test setting in IL)
* set timing to 2-4 degrees BTC @ 700 RPM
* set carb idle mixture screws adjusted slightly lean (1/4 turn in from normal performance setting)
* drive 30 minutes to warm engine and do not shut off in waiting line
* new oil and filter
* add Heat brand water remover (meth alcohol) to 10 gallons of gas
* new air filter or just remove it for test (max fresh air)
* new PCV valve or just remove it from valve cover (max fresh air)
Good luck. You didn't get these from me. :blueangel:
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Drifting
Joined: Jan 2002
Posts: 1,645
Likes: 11
From: Schaumburg IL
Re: Emissions Problems with 1981 getting UGLY (UKPaul)
One of the things I did not see in the posts is what dwell reading your mixture control solenoid is being pulsed at with the ECM. Before you start adjusting, put a dwell meter on the green T/P that is spliced off of the mixture control solenoid. Looks like a connector just sitting there. Set the dwell to 6cyl scale. If the carb is adjusted properly, the O2 is workling ok and the engine warmed up, it should be 25-35 degrees. If it is stuck on 10 degrees or at the 50 degrees you have a max lean or rich condition. The idle adjustment screws are normally set to 2-3 turns out max, and then the IAB adjusted to bring the dwell into spec. If you try to adjust the idle screws out for max vacuum (like pre 75 carbs) you will run a max rich condition and have HC and CO off the chart.
Also, put a vacuum gauge on the manifold. You should be pulling a strong pretty steady 17-20". Lower and you have retarded timing or a leak. Good luck and let us know what you see.
Also, put a vacuum gauge on the manifold. You should be pulling a strong pretty steady 17-20". Lower and you have retarded timing or a leak. Good luck and let us know what you see.
Burning Brakes
Joined: May 1999
Posts: 1,179
Likes: 0
From: waller texas
Cruise-In I Veteran
Re: Emissions Problems with 1981 getting UGLY (dsagers)
besides doing whatever needed to lean it out then add galon or so of colemans lantern gas.it is very high octane and have seen it used to pass emissions many times.Add the colemans then drive it around for it to mix good then take the test.you are close enough that it should pass then.
Drifting
Joined: Apr 2002
Posts: 1,743
Likes: 37
From: Stockton Ca
Re: Emissions Problems with 1981 getting UGLY (dsagers)
While you are chasing gremlins, don't forget the obvious. You said one plug wire was burned. How new are the rest? Also good spark will help burn ALL the fuel. New rotor and cap along w/wires can do wonders if your weak in that area. Sorry that I can't help more. There are additives spifically for help in passing emissions test.
Safety Car
Joined: May 2001
Posts: 3,758
Likes: 3
From: Surrey
Re: Emissions Problems with 1981 getting UGLY (VettePaul)
Are you still getting that marquee delivered ? :cheers: Paul
:cheers:
