I know the ecm has been covered in other forums and other posts but I haven’t been able to find an answer.

91’ Blazer stock 5.7 TBI

My issue is this. The ECMB fuse keeps blowing. I figure it’s a wire or component shorting to ground somewhere. I unplug the oil pressure sender/switch and the fuel pump relay to eliminate those. I was still showing a shorted orange wire using a test light. And I’m using the test light by gator clipping to 12v+ and probing the wire and the light comes on, in case anybody was wondering. Now, the thing that’s bugging me is this. The stays on showing a shorted wire until I unplug the ECM. when unplug one of the connections the light dims and when I unplug both the light goes off which is telling me that the ECM is the culprit of my shorted wire. However, when I decided to just just through a fuse back in just to see if it will blow again, nothing happens. The truck cranks right up and runs fine. I shut it off and started it back up about a dozen times and left it running for about 30 minutes and shut it down and started it right back up with no issue with the fuse. It kinda has me scratching my head. Does the ECM pin C16 and B1 get switched between 12v+ and ground??? Doesn’t seem right but I don’t know. Just need some clarification on what is going on with ECM.

 

In order to test a wire(s) for a short to power or ground that wire(s) need to be completely isolated first. You correctly removed the oil pressure switch and fuel pump relay from the circuit and I assume that the ECM b fuse was removed or blown but then you need to unplug the ECM so that all 4 orange power wires are isolated. Then you can use a test light to probe the orange wire(s) from wire to ground and then wire to power. With the ecm still attached you are simply powering it through your test light.

I would need to scan the rest of the wiring diagrams to see if anything else is powered off of the ecm b fuse circuit to really make sure your isolated.

George

 

I had a minute to check the power distr diagram. The Rear Wheel Antilock Module is also connected to that constellation of orange power wires from the ECM B fuse.


George