MY check engine light comes on while I am driving and the car starts to die (like I was turning the key on/off ) then the check engine light goes out and car runs fine. A mile or so down the road and it happens all over again. I checked the engine code and got a code 51. Says to check or replace PROM. MY question: can I just remove the computer or is there some special order I need to follow? I already have the battery out. Does anyone know of any test I can do to check this PROM thing? I just had the computer replaced two years ago, but I'm not sure if the guy also replaced the prom or used the old one. Really, thanks for any help. I am starting to dislike this car. Its broke more than its fixed.
This is on my 1981 coupe.

 

Richie, not that there is anything wrong at all with an '81 or '82, it's just as now these cars are becoming ""old cars that first came with computers"". An '81 is kinda by itself here as it was the only "computer carb controlled" Corvette produced, so the '81 will have a lot of it's "own" little problems, some of which you are experiencing. I was at an NCRS Regional where an ORIGINAL 4,000mi '81 could not perform it's "Performance Verification" test as one of the "sensors" was telling or not telling the carb to run so rich, even after it was fully warmed up and could'nt do it's "road test" portion of the judging because of the motor "stumbling" and rough idling. Also too, I was doing the Operations test portion of six '78-'82's. The three C3's with the "mechanical" alarm system worked as it should have. The three others(one '81 and two '82's), their electronic alarms completely failed.

I have seen '81's & '82's at several Corvette shows where it "appears" as the whole computer system was removed and the car "wired" up just like an older non-computer C3. Only downfall here is it's really illegal to do this(or OK if the car is raced, autocrossed, dragged-not licensed for the street). Also, especially if you have emission testing in your state, you'd never be able to do this. Probably the only real way to solve this is to find someone who knows these "earlier" carb computer systems with a diagnostic scope and sensor tester and can tell what's going on with your car. Maybe not the best advice OR cheapest, but that is what it may take to fix(temporarily repair???)your car :sad:

 

If the battery is disconnected, you can simply remove the ECM, just be carefull of static electricity. Code 51 in my book says "ECM circuit problems - faulty PROM, MEMCAL, ECM or checksum errors. In other words it doesn't nescessarily point directly to the PROM. Normally when ECM's are replaced on the older GM's the PROM is simply switched to the new ECM. There's really no way to check a PROM at home, Sometimes there is some checks you can do on the ECM, but not nescessarily. Before replacing your old ECM, find yourself a wiring diagram and varify all your powers and grounds are good, no shorts are opens that may damage your new ECM.

:cheers:
Pat Kunz

 

I had the same problem with my 81 when I purchased it. Code 51 and a few others. I left the computer in and removed and tucked all of the comp. controled carb wires out of the way, new holley 600 and a proform vac. advance distributor solved the poor performance...pulling the bulb out of the check engine light solved the orange light problem. I live in upstate NY so we only have visual inspection which is easy to get around. State run inspections will require you to fix the problem :(

 

yeah, you can remove the computer :rolleyes: i just hate seeing so many people doing this to these cars. as stated in an earlier post, you will have difficulty in licensing the car if your state requires smog testing. and if it doesn't, it will, you can count on that. also as stated, if you remove the computer, you will need to replace the carburetor and the distributor as both have computer controlled circuitry that control certain functions.
i do have a slight disagreement with some of what has been said previously. the first computer controlled vette was the california LG4 but it was a different computer. secondly, g.m. used computer controlled carbs up to '85 or '86, although not in the vette (i think they were still using them in trucks into the early '90s).
i am currently doing some research on what it would take to transplant a later model computer from, say, a '85 f-body into the early vette. these computers utilized many of the same engine controls but were faster and more reliable than ours.
i am currently dealing with an inoperative diagnostic circuit in mine even though the computer still operates the engine properly so i know they can be 'tempermental' to say the least.
i do not know if you can test a prom. i'm sure that someone can but i would imagine you need some pretty sophisticated tools to do so. i have a stock prom from my '81 but it is a 4-speed prom (no parameters for T/C lock-up). if yours is a 4-speed i would be happy to let you use mine for troubleshooting purposes.