ECM Short?

[Dayzedandkonfuzed]

Okay okay, not gbody related but close. I'm working on the neighbors 91 s10 and have found there is a short in the main feed to the fuel pump relay and oil pressure sender. Relay and sender unplugged, wire still shorted to ground. ECM unplugged, wire no longer shorted. So I've found that pins C16 and B1, which are battery power into the ECM and share the same fuse as the circuit in question, have less than 1 ohm resistance to the ECM case.

This is a problem right? Or am I going about this all wrong?

On visual inspection I have not found anything obvious on the circuit board

 

[78Delta88]

Just casual glance... Sounds like timer circuit on the board. I think it's a 555 or 556 which was common timer chip back then. If it overheated or failed, sounds like its acting like a Zenor or SCR and passing current when it should not be.

If the rest of the ECM functions are good..., the easiest would be hard wire 12+ through a switch on the dash to the OP sender in series and before the relay. There's a couple other methods, but that's the easiest.

You need someone that is really in deep understanding of the ECM circuit card.

There's a couple on Hot Rodders forum, not sure who would it be on GBody Forum.

 

[stew86MCSS396]

Not exactly following. Which wire is displaying a short to ground? Is it blowing the ECM fuse?

 

[Dayzedandkonfuzed]

Just casual glance... Sounds like timer circuit on the board. I think it's a 555 or 556 which was common timer chip back then. If it overheated or failed, sounds like its acting like a Zenor or SCR and passing current when it should not be.

If the rest of the ECM functions are good..., the easiest would be hard wire 12+ through a switch on the dash to the OP sender in series and before the relay. There's a couple other methods, but that's the easiest.

You need someone that is really in deep understanding of the ECM circuit card.

There's a couple on Hot Rodders forum, not sure who would it be on GBody Forum.

I have a pretty good understanding of electronics and circuit boards, at least enough to be able to do some testing. I ended up pulling it right out and following the circuit. First 2 diodes in line after the pin were fried, and they were obviously set up as short circuit protection. I couldn't definitively identify them, but replaced with something I thought would be suitable. Seems to have done the trick, eliminated the short and the truck is running now.

 

[stew86MCSS396]

You could probably teach me a thing or two!!! I would’ve just reached for the stack of ECMs in the parts room. I’ll finish up eating my crow!!! 🙌