91 Oldsmobile Cutlass Ciera quit while driving

ELPRUP

MEMBER
1991 OLDSMOBILE

3.3 V6, but that shouldn't matter.

The car quit while driving. It will crank, but not start. I believe it is the ECM because when it quit, then speedometer also dropped to zero. If this didn't happen, I would have suspected fuel or ignition. I want to confirm that it is most likely a bad ECM.

The ECM and other fuses in the fuse panel are okay. The fuel pump doesn't prime when the ignition is turned on (bad ECM's fault?). The initial dash lights do come on when the iginition is first turned on (not under of the ECM's control?)

I haven't checked for spark or fuel, but I'm hoping that the speedometer going to zero at the same time it quit specifically narrows the issue down to a bad ECM. If my assumption is correct, can I get away with changing a relay or should I just swap the whole ECM? I can get an ECM for $40. How much is the relay? The only problem is that I fear the ECM I'd be getting isn't KNOWN to be a working unit.

If my assumption is confirmed, then it will do two things for me. First, it would tell me that I wouldn't be wasting $40 for nothing. This part isn't really a big deal; I'm willing to risk $40. The second thing is that if the speedometer going to zero when it quit specifically means that it is my ECM, then I'd know that the ECM I swapped in was also a bad one if my car didn't start after the swap.

Thanks for your help.

1 Reply

CHEVY22

MECHANIC
1,375 POSTS

There are alot of things this could be, I never suspect and ecm, pcm vcm or tcm until I have checked everything else, your gonna have to dig in and do some testing, check the f/p relay if that is ok check for power at pump should shoot 12v for 2 seconds and work from there, but like I said there are 100 things it could be, ecm needs input signals to start and run the engine and if it loses one bam, start simple, fuel, fire