Troublecode 51 from ECM at 1980 Firebird

Hello at all!

I have a 1980 Pontiac Firebird Formula with 305cui LG4 "H" engine, Rochester E4ME carburetor, o2-sensor, air pump and c4-system.

The gas mileage is a little bit high. 16 miles per gallon equals. The spark plugs are very soot-black, the exhaust gases smells at a rich fuel mixture.



When i check the trouble code, it flashes 5 and 1, therefore it is 51. The GM-manuals says PROM-failure.




So good i can do, i have controled all the sensors, wires and solenoids, have controled the PROM seat.

My Problem is, i don't know, is the ECM and the PROM the right for my car. The ECM seems to be refurbished in the past.

They are lists with numbers, wich ECM and PROM are in wich cars?


My Numbers are:

The PROM is an delco 1337 AL, the ECM an 77-4670

I hope, you can help me to eliminate the failure.

Bye, Alex

hey there alex

a 77-4670 is definitely a "remanufactured" cardone ECM, so it's probably junk.

get a good used GM one that hasn't been disturbed

your local auto wreckers probably don't have any, but ebay has lots of new old stock ECMs. part number 1224670, i think

honestly though your best bet is to either:
- convert to TBI
- throw the computer and that rochester in the garbage and just put a normal carb on it

Hello steveo,

thank you for answer!
How sure i can be, the PROM 1337AL is the right for my car?

Hello all,

i have find a used GM ECM with prom from a 80th. corvette. The engine ligt is off, the gas mileage sunks from 20L. to 15L. / 100Km. Now i have a little bit problems with cold start and speed up at 50 - 60Mls, but i'm sure, these failures i will be eliminate the next time.

Thank you for help!

Alex