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I take my 81 out for a spin and everything is fine until it gets about 15 minutes in and my check engine light comes on and the idle either gets rough or stalls out. I checked the code and it comes up 23. The shop manual says code 23 is the mixture control solenoid. It says to check voltage at M/C solenoid, if over 10 volts, I got 12v, check voltage at ECM terminal 18, I got 12v, if over 10 volts check Carb M/C Sol resistance. I got 23.6 ohms. Last block says faulty ECM connections or ECM. Checked connections and they were good. Ohms ok no grounds. I checked the solenoid with voltage, it picks up and with the car running as best I can tell it is operating ok. Clicking on and off. Is the ECM intermittent? As soon as the engine cools down everything goes back to normal. Any ideas?
I don't know if this will be helpful. I've recently fixed several low-tech computers in cars that had failed capacitors and/or solder joints. Symptoms are often temperature dependent, so failing caps are cold sensitive, and bad solder joints are heat sensitive (more likely to be your problem). I don't have an 81, and I don't know if anyone is selling rebuilt/refurbished ECMs, but there probably isn't much magic to them if they are. I searched for related terms, and couldn't even find a picture of your ECM's circuit board.
You could try to repair and/or replace the ECM. Maybe you get lucky, and find a writeup on how to do the fix online, or find one for cheap, and it fixes your problem, today.
Possible long-term options include removing the 81-only ECM. Many on this forum have swapped back to the 1980 setup (M4ME Q-Jet carb, or a good Holley or older Q-Jet with an electric choke, and an HEI dist with a vacuum advance). Or if you think you'll swap to programmable EFI anyway, now might be your chance!
Thanks, good options. I think my next move is replacing the ECM. People keep telling me to get rid of the Q-Jet but I like to keep things as original as possible. Ecklers was like $100 but you have to use the old prom. I agree it sounds like it’s heat related just need to track it down. Thanks again.
Thanks, good options. I think my next move is replacing the ECM. People keep telling me to get rid of the Q-Jet but I like to keep things as original as possible. Ecklers was like $100 but you have to use the old prom. I agree it sounds like it’s heat related just need to track it down. Thanks again.
I hope it works for you! Please update us as you go, and please post some photos if you can.
Threads that show solutions help lots of Corvette owners, including many who never post here.
Welcome to the Forum, I hope you can fully enjoy your Vette soon!
You mentioned that 'connections were good' on your ECM. Did you separate all the connectors for it and clean all the contacts? And did you remove any grounding point connections and clean them well (sand the surfaces, etc)? You must do that first; it might save some wasted expenses.
If you do this and you still have code 23 fault, it could well be that the mixture solenoid is 'giving up the ghost' (after 40 years of service!).
I removed the connector for point 18 that’s where the block diagram led me to check. I’ll go back and do like you suggested, sand ground connector, I’ll also remove other connector and clean that too. I used contact cleaner but Someone said use De-oxit, I have to order some.
Thanks for the advice. I have a good friend told me he actually use to rebuild Q-jets he said he might stop by. I would need him to help me with getting that solenoid replaced. Process of elimination
i am gonna add one to dump the ecm, carb and distributor side. it is 40 year old bad idea. was designed to get cars through emissions so GM could sell the cars. not so the cars would hold up a half a century. i know, that applies to everything on these cars, but this was the first attempt at computer controlled afr. and now you are trying to rely on 40 year old ecm. as long as programming in your prom is ok, and probly is, a replacement ecm may work. but a vacuum-centrif distributor and a fresh good q-jet doesn't have any 40 year old electronics to bite you on the ***. more recent emissions components are federally mandated to be warrantied for 10 years. and your setup is one of the reasons for that mandate.
derek...
Would you buy a new car and ditch the ECM? No, I think not. Even though the '81 engine management system was the first such effort on the Corvette, it was still an improvement over a carb and distributor for most applications. It did a respectable job of regulating A/F mixture and adjusting timing to a better-than-the-old-system level. If the OP has a working system, it is probably better for him/her to maintain it, rather than spend more money and time to back-track to a "lesser state". Just sayin.......
23 code
