I have a 81 vette that i am chasing a problem with. The car runs fine when its first started up. However, after its warm it will randomly start idling rough at red lights and the volt meter plunges to right above the red. This is with a/c and/or headlights on. I turn the headlights and/or a/c off and the voltage returns to normal but it continues to idle rough until i turn the car off then turn it back on then its back to normal for a little while then it starts it all over again. I orginally thought electrical so I replaced the alternator and ran a new 10 gauge wire from the alternator to the battery cable stud on the starter. i also replaced the voltmeter thinking it was the problem. but alas it does the same. So I thought maybe the idle was too low so i turned it up some, that was a no go also. Now I am leaning towards fuel system. What exaclty does the computer control in a 81 vette? could it be part of my problem?

So to recap.
starts and drive fine a/c and/or headlights on
warms up then at random starts idling rough (give it some gas it smooths out)
when it idles rough the voltmeter drops to near red
turn off a/c and/or headlights voltmeter returns to normal but still idles rough
Turn engine off even for a second then start everything is normal until it does it again at random

 

Computer Control Modules are sensitive to voltage variations. I would suspect a loose cable or bad ground somewhere. With older models I would suspect the ignition module in the distributor and a low voltage problem, but not sure how an '81 works with the computer, etc.

 

Just a thought is the carb bolts on top nice and snug .Put a volt meter right to the battery while idling , should have 14v or so .

 

Sounds like you may have one problem causing another. For your voltage to peg, it would seem like the internal regulator might be bad, probably when it gets hot. I'd check the alternator out first. That kind of voltage could cause the computer to go into a full rich condition (limp home) which would re-set when you shut the car off. Are you getting the check engine light at all?

 

Couple of things:
When it started running rough at idle the idle speed no doubt dropped, when that happened the voltage from the alt dropped from low rpm. If you bumped the throttle a bt it would come back up.
The E4ME carb that is supposed to be on that carb gets a bad rep because most guys don't kow how to work on it. Most of the ones I have seen had issues to to mis adjustments and mods by monkeys. I would start with all the vac lines, make sure they are all secure. Go through the carb setup, this requires a couple of special tools. Once you have all the common stuff eliminated, then look into the other things like the O2 sensor, TPS and the like. Do not use an ohm meter on the O2 sensor, voltmeter only. The TPS is a potiemeter so an ohm meter there is ok. The F/A mix solenoid is ok to use an ohm meter on.
This thing will be an education, but its worth learning

 

Ok i checked the ground from the motor to the frame and the frame to the battery both looked good and tight. the bolts on the carb are good and tight. when it running correctly at idle with nothing on im getting 14.25 volts at battery, 13 at gauge, 14.5 at alt. with a/c and headlights on im getting 13.5 at battery. little less than 13 at gauge and 13.5 at alt. the alt is brand new but i know new ones can be bad out the box. but the alt before did the same exact thing. if i give it a little more gas when its running crazy it does smooth out and the voltage returns. my tach isnt reading 100% correct so ive let to put my timing light on it to give me correct rpms. upon further inspection i found a coolant sensor with a round connecter that was cracked at the base. i ordered a new one should be in tomorrow. could that sensor have anything to do with my problem? also the wires to the connenctor for that sensor were bare in spots so i taped them up with electrical tape so they wouldnt touch each other nor anything else. i plan on getting a new connector next week.

 

So you eliminated electrical as a problem. Now step through the rest of it, vac lines, check the sensors, run the disgnostic codes etc..

 

Also, to fully check the carb out, you'll need a dwell meter too. That will tell you alot about how your carb is working. You can find those procedures in the service manual. If you don't have one, you should really consider getting one...

 

whats a dwell meter where can i get one how do i use it?

 

how could i tell if the torque convertor lock up is stuck? because it works fine in neutral or park but in gear. it runs rough

 

How do you tune a carb with a dwell meter?

 

update

it cant be the lock up because this trans doesnt have the connector for it. the wire from the computer is zip tied up in the harness.

also! at idle i looked down the barrels of the carb and i can see gas dripping down. im pretty sure thats not supposed to do that.

 

Here is a link for your E4ME carb.:

http://www.thirdgen.org/techboard/ca...e-rebuild.html

 

I'm thinking if doing away with the computer all togeather carb off a 79 and a new hei dizzy

 

best thing i ever did and have not looked back since.

 

These particular carbs use a dwell meter to measure if the computer is in open or closed loop and how the mixture control solenoid is working. There's a green connector usually near the electric choke that you connect to. 81's are the only vettes with this set up.

 

I took a different approach. I kept my carb, just changed everything under it!!

 

Thanks for all the help guys im going to elminate the computer!

 

Thanks for the info. Gary