I know there's lots of people who would remove the ECM and harness, change out the CCC, Distributor and manifold. Not interested. I restored my 81 Corvette 11 years ago. I put it back all original except for the AIR smog equipment and added a 700R4 and crossmember. Original motor bored over fly cut heads stock cam. Also installed a newly rebuilt E4ME, D.U.I. distributor and remanufactured Cordone ECM with a Hypertech Phase II prom with 160 thermostat. I had straight duals ran with a new 02 sensor.
The car has ran a little rich but good for 10 years until recently, so I have been trouble shooting for a month. The Service Engine light Started blinking and the M/C solenoid was sporadic. It ran rough and would not run with the 4 wire ESC connected. No codes would show on the ALDL, just constantly blinking. So far I have replaced the choke thermostat which was cracked around the edges. I installed new plugs, new distributor cap and button. I replaced the Dyno Mod ignition control module with a new AC Delco module. After all that no change.
Then I replaced the Cordone ECM with a AC Delco 1224810 remanufactured by GM. I replaced the Hypertac prom with the original AC Delco prom. Also the 02 sensor. 🤞 I turned the switch on and the service engine soon light was on solid. She fired up and the light went off with no code so far. 😃
She seems to be missing now up to 1500 rpm and the tach is fluttering a little as it misses. I have 11.77v at the Dwell hookup. 😢 I am getting frustrated because I have done all this work plus cleaned the grounds, double checked hoses, wiring, new tach board and filter. The carb was rebuilt for the second time about 2 months ago and tuned per Lars Grissom's specs. Today I will recheck timing to 8.



If anyone has experienced problems like these, please feel free to comment. I live in Acworth GA if someone knows someone in the area that is a good old school GM mechanic.

 

Sounds like you need to adjust your carburetor. I could not get my 81 running right until I rebuilt my carb myself. Most carb builders set these up without a CCC test engine and set them up as standard Rochester carbs. Ask me how I know. After returning mine 12 times to a local rebuilder I researched and rebuilt it myself. Try to pick up an OTC Monitor 85, that is the same originally used on these cars. I picked one up on ebay and got my car running great, and use it for maintaining. It looks like your air bleed screw is screwed down way too deep also, it should only be around two threads deep. That would cause it to run rich. Also look for vacuum leaks. It is a balancing act between the two air bleed screw on the bottom and the large air bleed in the middle on top. There is also correlation between the lean and rich stop screws as well as the mixture control solenoid screw. The rich and lean should be set up when the carb is rebuilt and apart. They can be adjusted after but a little more difficult. I have also done it after though and it works.

four turns out is the starting point for the idle mixture screws in the front of the baseplate.

The Mixture solenoid screw - the one that sets the depth of the mixture control solenoid coil in the fuel bowl (aka the lean stop), is initially set with a Thexton 403 tool.

If you dont have the tool, you can measure 1.303" from the base of the primary jet tube (where it enters the brass part of the primary jet) up to the underside of the mix control plunger (holding the plunger all the way down in the solenoid by hand).That's the standard start point for tuning

Depending on your carb the rich stop may be automatically set via a small aluminum finger on the screw, or it may be a separate adjustment in the air horn in which case you are looking for about 1/8" travel of the mix solenoid plunger from rich stop to lean stop. Check for this travel once the air horn is installed. There is another thexton tool for setting the proper initial air bleed depth as well.

Then its a matter of hooking up a Dwell meter on 6cyl scale and tuning the air bleed and mix screws.Tune when engine is hot, and try to get a 25-35 dwell (it should vary a little back and forth) va the air bleed. If you cant get it there via the air bleed then you need to adjust the idle mix screws a little bit lean or rich as the case may be and then fine tune again with the air bleed. All the time watching the dwell meter.

Think of the mix screws as BIG adjustment and the air bleed as FINE adjustment.

I still have the original exhaust set up for the exhaust, y pipe to Magnaflow High flow cat, to y pipe to the mufflers. I have the air pump removed, but still run the CCC and O2 sensor. Did you see any performance gains by going to the true dual exaust and eliminating the CAT? did that also cause any issues with the CCC and Check Engine Light?

 

You 'da man, Reaper... That detailed info should get the carb working better. Hope that's all it is.

P.S. If the CEL is now 'off' when engine is running, the system has no "major" issues. Some adjustments may be a bit out of range, but not enough to throw a code. Rebuilding the carb is a good place to start, based on the symptoms your are experiencing. Good luck...

 

I guess I'm going to pull the Carburetor again. I just rebuilt it again last year using the shop manual and a few Lars adjustments. I'm not getting in any hurry this time.
I did notice the upper air horn gasket is soaked.

I have a Code reader 85. The ALDL and the 85 both read code 12. So no help there.

 

I am running a few test before I pull the carb. I cranked her up today with the dwell meter hooked up and it was reading 30. Then it started to gradually going up to 54.