90 Suburban ECM Fuse Popping

[Bright Idea]

Update
More than a year has went by and I finally pinpointed and repaired the problem. The ECM B fuse popping was a very random pattern sometimes related to hitting a hard bump and sometimes not. 2 weeks ago we had a significant snow event and the problem went from intermittent to regular. This helped identify it in that with the snow melt over the firewall it became apparent that there was likely something going to ground and the moisture that was in that area from the melting snow was contributing. On Saturday I took it for a drive and only had one fuse blow in probably a 20 mile trip. Upon return, with the engine running i did some jerking around of the harness on the drivers side as it runs toward the rear of the engine under the distributor and above the bellhousing. with some significant movement I cause a fuse blow. Long story short, in the nested main harness it appears that where the orange wire connected to make a drop to the oil pressure sender they had left a sharp tail when it was crimped, this had worn thru the tape covering it and the loom cover had deteriorated from heat. Evidently this was positioned against metal and either a bump or moisture could complete the contact to ground intermittently. I cleaned up and taped the connection and recovered the harness with new loom cover. I have driven about 200 miles since over some of the roughest roads close by and have had no more fuse issues.
Talk about a shot in the dark. I am relieved to have this issue resolved. On to the next.

 

[Cuba]

Update
More than a year has went by and I finally pinpointed and repaired the problem. The ECM B fuse popping was a very random pattern sometimes related to hitting a hard bump and sometimes not. 2 weeks ago we had a significant snow event and the problem went from intermittent to regular. This helped identify it in that with the snow melt over the firewall it became apparent that there was likely something going to ground and the moisture that was in that area from the melting snow was contributing. On Saturday I took it for a drive and only had one fuse blow in probably a 20 mile trip. Upon return, with the engine running i did some jerking around of the harness on the drivers side as it runs toward the rear of the engine under the distributor and above the bellhousing. with some significant movement I cause a fuse blow. Long story short, in the nested main harness it appears that where the orange wire connected to make a drop to the oil pressure sender they had left a sharp tail when it was crimped, this had worn thru the tape covering it and the loom cover had deteriorated from heat. Evidently this was positioned against metal and either a bump or moisture could complete the contact to ground intermittently. I cleaned up and taped the connection and recovered the harness with new loom cover. I have driven about 200 miles since over some of the roughest roads close by and have had no more fuse issues.
Talk about a shot in the dark. I am relieved to have this issue resolved. On to the next.

You are awesome for posting an update! Can't thank you enough for that! Even more importantly, you finally resolved your issue. Well done!

 

[gmbellew]

I'll add my experience to this post to help others. I had 2 spots on this 440 ORN circuit that rubbed through to ground and caused issues. The first, and easiest to find, was on the MAP sensor bracket. The second, and harder to find, was on the back of the cruise control bracket. hope this helps somebody...the "wiggle" test works!