View Full Version : Possible bad ecm?

Devils Toy
01-07-12, 12:32 AM
Ok guys I have a good one. 82 collectors editions that fires right up but idles like a big block with a dead cylinder. CEL is on. I get the usual dtc 12 then nothing else, using the paper clip method. To my knowledge the motor has been rebuilt. I have found no timing chain issues. When I try to adjust timing ( brown wire disconnected) it starts to smooth out but when I crack the throttle it stumbles. When I check timing marks on the balancer ,when I get it to idle smoothly, the mark is no where in sight. When I put it back to 0 it runs rough. The distributor is new(had one laying around). When I connected my snapon scanner to it, it says unable to communicate with the car. I have checked the ecm fuse on the fuse block and it is good. To my knowledge there is another ecm fuse by the battery. Now if I am right that fuse is also for the fuel pump. So if that is blown then the fuel pump WILL NOT run, correct? So the ecm is bad? Any input would be greatly appreciated.

Hib Halverson
01-07-12, 10:48 AM
You're right on the pump fuse. If that's blown, the engine won't run.

As for the misfire, you didn't say if it was random or the same cylinder all the time. I have an 82 CE that after cold starts, usually runs rough, but after a minute or so, even before closed loop, it idles nice.

If the cam timing has not jumped and the dist. is in right, it's possible the outer ring on your balancer has "spun".

Best way to check is to find TDC with the positive stop method then see if the timing mark on the balancer lines up with the zero on the index plat on the timing cover.

As for your MIL on but the system only flashing DTC12 and your Snap-On scanner not communicating with the ECM, if the Snap-On supports 1982 GM vehicles, then the ECM might be bad but first, just in case, I'd look for an open or a short in the serial data line.

You'll may need the 82 FSM for its wiring diagram.

Devils Toy
01-07-12, 11:16 AM
That was another thought. I had that happen to a big block. I had checked that to see if that outer ring had spun but not that lucky. The missing is random. I checked plugs ,wires, compression but everything seems to point to the ecm.