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Discussion Starter #1 (Edited)
I need help my ECM-B fuse (10 Amp) continues to blow and I need ideas of where to start looking for the short. This is an 89 suburban 4x4 350 TBI.

The first three times this happened it would only occur when I was in reverse, I would swap the fuse and things would seem to be fine for a while. I took 1.5 hour trip with no problems. I didn't worry much becuase I don't use the truck much and it didn't appear to be a problem when going foward, until today...

I was on my monthly trip to the municipal yard-waste site when turning in to the drive..bam...truck shuts off. I knew it was the fuse but was worried becuase this was the first time it happened when driving foward. My fears were warranted becuase after I inserted a new fuse it blew instantly when I turned the truck on.

I went through 3 fuses before it occurred to me that the problem use to only occur in "reverse" maybe the problem is happening in "park" gear position now too. So I shifted to nuetral and tried a new fuse. It worked!! Truck started so shifting seemed to shift or adjust the shorted wire to eliminate the short. But then I went out to shut the hood and the engine killed instantly. So it was a short-term fix and shutting the hood wiggled the wire enough to cause it to short again.

After the single glimmer of hope that was dashed when I shut the hood, the fuse now blows instantly no matter what position I have the gear shift indicator. I had the truck towed home so I can begin the investigation. But I could use all advice both specific to this problem and general advice for finding shorted wires.

Becuase it seems related to my gear shift indicator and steering and the general steering column area What major wires could this be? It is the ECM-B fuse..which is the battery feed to the ECM. So whatever wire has the short, it is it is related to the ECM. Does the gear shift indicator go to the ECM?

All insight or advice appreciated...

Sincerely,
Nate
 

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Discussion Starter #2
Transmission Position Switch

So in looking at my wiring diagrams I see that the transmission position switch is a ground path to the ECM. Has anyon heard of tranmission position switches going bad? If it is a ground path for the ECM is it reasonable to assume that a short in the switch would cause my ECM Battery fuse to blow?
 

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Nate - I don't have specific advice for this issue, but in general electrical issues are no fun to troubleshoot. I just recently corrected an electrical issue in one of my non-chevy vehicles.

Sounds like you're starting in the right place by looking at the wiring diagrams. It's a PIA, but disconnect every component on the particular circuit that is shorting the fuse. Then put a good fuse in the fuse box and starting at the rear of the vehicle (longest runs of wire) begin plugging components back in one at a time and check the fuse for continuity between each component plug-in. The component that blows the fuse is the culprit. Then you can concentrate on the wiring for just that component.

Sorry, I'm not familiar with the '89 burb and what components are on the circuit for the ECM-B fuse.

Good luck.
Emile
 

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Discussion Starter #4
Thanks Emile,

Now I have a new problem, the short is intermittent, so it seems to come and go with no pattern. When the tow truck dropped my truck off I put in a new fuse and whola! it worked. Then I dirve up and down the driveway...and poof...shuts off again. I can jiggle wires and I've really looked all over and cannot find any wires on exhuast manifolds etc. I climbed up on top of my engine last night and was looking back behind the engine at the main wiring-harness, I see no obvious issues.

I have noticed on the wiring diagram that the ECM-B fuse seems to be related to the fuel pump and fuel pump relay. I wonder if something with my fuel pump could be shorting? in the tank? I can't quite picture how this would be...but anyone ever hear of something like this?
 

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Where do you live? It could be a winter related short somewhere from road salt. Have you taken the fuse block off the fire wall or the one in the motor bay and turned it over to look at them?
 

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Discussion Starter #6
Thanks Enkei for the idea.

I have not pulled the fuse panel off the wall yet, I only have one and it is under the drivers-side dash things are very clean and dry there so I can't image there is rust behind it, but I may peek just to see anyway. I have a more dtailed wiring diagram now and it seems the only thing on this circuit are
1) Fuel Pump Relay Harness
2) Oil Pressure Switch (which is also a fuel pump switch)

So I have a smaller wiring path to focus on now, but coming off the fuel pump relay harness is a power line for the "Fuel Pump Prime Connector" which I assume is the main power to the fuel pump?

I really don't want to lower the gas tank as it has a fair amount of fuel in it..but I may not have a choice.
 

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1990 GMC Jimmy "JimmyRig" 350 1 ton swapped 37's
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Hi, Nate. Did you ever resolve this issue? I am having the exact same issue as you describe above on a 1990 GMC Jimmy, 5.7L/350 TBI. I've been doing everything that you stated above and still scratching my head. I even ran a temporary wire from the fuel pump to the battery and it ran fine and drove for about 3 miles then blew 4 fuses in about 5 minutes before I parked it and started troubleshooting again. Any advice or direction would be greatly appreciated!
Thanks, Travis
 

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‘01 Silverado 2500HD 8.1/Allison 5sp xcab long bed
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Start with unplugging your oil pressure sending unit. It’s on the same fuse. If it solves your problem, it’s the pressure switch failing and shorting inside. I had this happen to me.
 

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1990 GMC Jimmy "JimmyRig" 350 1 ton swapped 37's
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Thanks, Greg! That is exactly what I am doing today. I will post again if that fixes it.
 

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1990 GMC Jimmy "JimmyRig" 350 1 ton swapped 37's
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Start with unplugging your oil pressure sending unit. It’s on the same fuse. If it solves your problem, it’s the pressure switch failing and shorting inside. I had this happen to me.
Thanks for your suggestion! JimmyRig is running again. It was the oil pressure switch and I was chasing the fuel pump the whole time.
 
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