1981 Avanti 11 Smog issues or sensors?

[g2watch]

I just bought a 1981 Avanti 11 and it runs rough. I have replaced the Carb, fuel pump, plugs, pvc vale, vacum hoses and I have ordered a new EGR valve. The car runs and get worse the longer you run it.

Anybody have any suggestions on what type of sensor to look at next.

This year has the most smog related stuff I have ever seen on a 305 Chevy.

Thanks,

Ray

Edited May 6, 2009 by g2watch

[Gunslinger]

There's a number of things it could be, but long distance all anyone here can do is provide some suggestions. You've already changed a bunch of parts but that's kind of a shotgun approach.

In 1981 model year GM began using a computer controlled carburetor and if the carburetor is replaced with the wrong model the computer will malfunction, or the computer could be the culprit by having gone bad. I don't know if Avanti Motors began using the computer controlled carbs at that point. They may have had enough crate engines on hand before installing the computer controlled carbureted engines. If your car has that kind of system, it would need to be completely disabled. It could be your whole problem. If you do have a computer controlled carburetor, it may have an oxygen sensor in the exhaust pipe and that sensor could be bad.

Outside of that, there are a number of other issues. You could have a major vacuum leak. What kind of vacuum reading do you get from your gauge? That can tell you a lot. The intake manifold could be leaking or from some other location. The EGR could be bad as you already have thought of.

You could have a bad distributor cap and/or rotor in the distributor. The electronic module inside the distributor could be bad...it's been enough years and they do go bad. The coil itself could be bad, though not as likely as the module. All of these are an easy fix and not very expensive. You didn't say so, but the plug wires could be part of the problem as well.

You could have a blown head gasket or even a cracked cylinder head. Check your oil dipstick and see if it smells of coolant or even an excessively high level of fluid. If it does, you have to find which cylinder head might have the problem. There's ways of testing with diagnostic equipment, but you can pull spark plugs and see if any are coated with glycol. If so, you'll find two adjacent plugs are likely coated. It's between those two where a head could be cracked or a gasket blown. If this is the case, get it fixed pronto as ethlene glycol does not like engine bearings.

You could have a clogged catalytic converter or some other restriction in the exhaust system. I've seen exhaust pipes look good on the outside and be collapsed internally...rare but it does happen.

There could be other areas to look at but work on the simplest first and see where that gets you. I hope you find it's a simple solution.

[g2watch]

Gunslinger,

Thanks for the heads-up on my issues, I have taken the car to a good mechanic and he believes it is the electronics and maybe the carb.

I will keep you posted.

Regards,

Ray