Hey all,
I just recently bought a 1992 with an lt1 that had been sitting for quite some time. I had to replace most of the fuel system and fluids but once i did she started right up. Took her for the first drive and right at 3000 RPM she wants to cut hard. At first it seemed like a miss but its more severe than that. The diagnostic codes read as follows:
module 1: c41, h41
module 4: ERR
module 9: h72
Service ASR and Service Engine Soon lights are both on.
Radiator fans kick on right away when ign is switched over to ON, seemingly no power to the AC controller, and security light blinks incessantly. I cannot leave the battery connected because it will fully drain in only a few days and no lights are on that I can see and i've looked pretty hard...
Now here's the kicker, last week I tried reading codes again and module 4 read no ERR and no codes. But now the error is back. So maybe its just a connection issue?
I am brand new to corvettes and an intermediate mechanic so any help would be greatly appreciated. My thoughts are a faulty ECU but my friend that I bought it from said he had a new ECU put in only a couple years back and it is an original computer.

 

Those codes certainly point to either a faulty ECM or faulty connections to the ECM, yes.

 

Haven't yet been able to get my hands on a new ECM but i read a few threads saying that it is temperature related problem. I live in Florida so temps right now are always above 80 Fahrenheit. Some guys said if you stick your ECM in the freezer then plug it in your error and code 41 might go away. So I gave that a whirl. Yep... after it had been in the freezer i plugged it back in and absolutely no codes set, speedo works, everything works and i took her out for a drive. screamed past 3k rpm no problem. only lasted about 30 min until it warmed back up. Seems I definitely just need a new ECM. Anyone know of where to get my hands on a (likely) reliable ECM for a 1992?

 

My 93 was doing the same thing. Started out fine but when it got up to the point of the 2nd fan cutting on, it felt like it dropped 4 cylinders, backfiring and popping and the SES light started flashing. 92 and 93 ECMs have a problem with the soldering on the printed circuit board. I sent mine to SIA electronics and they reflowed the board and tested the ECM before sending it back. Cost e $250. Turnaround was really quick. Car now runs like new.

 

So I just got my ECM back from being reflowed at SIA and I plugged it back in and im still reading the same codes and errors I had before. Im really stumped now.

 

Looks like it's time to go hunting into the ECM harness and see if there are circuit faults. It's a major PITA to do, but the wiring to the ECM is the next possible culprit, all other things being equal.

 

Normally I would agree but if i stick my ECM in the freezer it will work fault free for 30 mins. This leads me to believe it is simply the ECM that is the fault in the system.

 

So wait, SIA just...reflowed the solder and nothing else? That seems like a waste. I'd expect an ECM place to actually look for and repair faults.

With that new evidence then yes, I agree, the ECM is still bad, and clearly the fault was not cold solder joints.

 

So i went to go test my car this morning and when I turned the key the error codes came on then went away and then came back (its easy to tell because the fan turns on when the codes set). I opened the small lid on the bottom of the ECM and found that SIA didnt fully reconnect my PROM and it was only half way connected and sort of dangling there. So i connected that back up and now it is running great. I know for a fact that before I sent it to SIA the prom was securely fastened. SO i guess the tech that laced my unit back up just made a mistake or it got knocked loose in shipping. Regardless it seems that SIA DID in fact fix my ECM. Hopefully she holds together for me.

 

Heck yeah!! I thought it was really odd that they wouldn't considering they have glowing reviews here on the forums. So glad to hear it was something simple!