This is the 3rd board I've posted on concerning the same problem. The engine s but won't start. It just won't fire. I was screwing around with the manifold and whatnot, and when I put it back on I forgot to put one of the ground straps back on that goes from the firewall to the manifold. I was told that ground strap grounds the ECM and all the electronics. If that's the case then I royally screwed something up when I tried to start it with the ground strap off.

Anyways, I had an extra ECM from an 87 Firebird and decided to try out its PROM in the new ECM that I bought and it threw a Code 51. So after that I put the original PROM back in and there is no code at all. Other than a bad wire somewhere, I've narrowed my problem down to a bad PROM. My question is, if the PROM is bad/lost its memory will it always give a Code 51? Because I'm not getting a code.

I also saw someone post that if the check engine light doesn't come on with the ignition in the "On" position then that means that the ECM or PROM is bad. If that's true then it has to be my PROM because the ECM is new. Can someone help me out a little here?

 

1985 FBody uses a 1226870 ecm. A 1987 FBody uses 1227165 ecm. Not interchangeable IMO. Same on proms.

To check if runnin on prom do "key on engine off" you will get a blink of CE light then come on solid. Code 51 is prom. First step make sure it is in correctly(not backwards) if code comes back after erasing code then next step is to consider the ECU being faulty. That is from service manual.