'94 CPI: ECM1 fuse blowing

Having a recurring issue where the ECM1 fuse blows while I'm driving, killing the engine. This is the fuse for the ECM, EGR, and injectors. It blows the OEM 10 amp fuse within a minute or two and takes longer for a 25 amp. I haven't had a chance to really tear into things yet - does anyone have any thoughts?

Injector wires are kinda small and I've had a broken wire issue in the past. see if you can trace the power wire on those possibly grounding where they shouldnt be.

How good are you with a multimeter? If not very, it is looking like now is a good time to learn haha

Start measuring the resistance on the circuits from the fuse and checking to ground to see if what Ryo mentions is true. That's about the only way I've ever discovered the problem in a situation like that and I'm glad I finally learned to use the multimeter effectively in those cases.

One small helpful thing I've discovered while diagnosing electrical issues; most fuses have the terminals poking through the upper plastic casing. Makes it much easier to touch the probe to either side. This guy does a decent job showing it: https://youtu.be/iG-AsEemqD4

Good suggestions and link, thanks guys. I'll start poking around this weekend and see what I can find. I'd say I'm a novice with a multimeter - definitely not an expert but I have checked and diagnosed a few things on the truck in the past.

The one complication may be that it's an intermittent problem and it seems to run perfectly before it dies. Would the best thing to do be to check the resistance on the circuits right after it dies with the idea that the wire will be shorted out then?

The second complication is trying to find 5 free minutes to work on it with a new baby in the house.

Here's a tool to make it easier to check the draw on each circuit.

http://www.harborfreight.com/30-amp-automotive-fuse-circuit-tester-67724.html


Put that in, then connect/disconnect branches of the circuit until you find the branch thats drawing too much.

The only thing I can unplug without killing the engine is the EGR though, correct? I still haven't had time to even pop the hood so I'll stop bench-wrenching now and get back to you then!

The drain or over-current may be happening without the engine running, so just turn the key to ignition without starting to diagnose the circuits to begin with.

I spent about 20 minutes looking through the wiring on the weekend and nothing looked out of the ordinary. I didn't have a chance to completely remove the covering from the harness though. I know I'm looking for the pink/black wire and I wasn't able to follow it fully from the cab to the end of each circuit. FWIW, it starts up fine and idled for 15 min while I messed with it.

I figured out that it only blows the fuse when the engine reaches operating temp so I'm suspecting EGR. I unplugged it and will drive it for a while to see if that takes care of it.

I hate electrical issues... It's now at the shop and they haven't been able to identify the issue yet either. The shop owner's son is a GM tech with an electronics background and he's going to take a stab at it after hours.

Ended up being a burned wire right in behind the passenger side head. It required removing the distributor and a bunch of other bits and pieces to track it down.

Glad they found it, but it was certainly trying its best to avoid detection.