Author Topic: ECM-B fuse keeps blowing - 1991 SUburban  (Read 67 times)

Offline tyekid

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ECM-B fuse keeps blowing - 1991 SUburban
« on: April 06, 2021, 05:09:34 PM »
Hey everyone,

This past summer, I purchased a Forestry Service '91 Suburban. The past owner had mentioned fuel pump issues, so the shop I bought it from had already replaced the fuel pump. For a while, everything was going pretty smoothly. I even took the truck on a 1,000+ mile road trip down and back up the West coast without issues.

Right after I got back, I took my truck to work. When I went to leave, the engine would turn over but not start. The fuel pump did not seem to be getting any power. The ECM-B fuse had been blown, and any replacement fuses would immediately be blown when I began to turn over the engine. I ended up replacing the fuel pump relay and the oil pressure sending unit, which seemed to fix the problem.

A couple of weeks ago, I was on my way to visit a friend's house. I hit a speed bump a little harder than usual, and I immediately lost power. My ECM-B fuse had blown again. Currently, the replacement fuse is working, but I'm afraid to drive the truck anywhere before this issue is resolved.

At this point, I am mostly interested in bypassing the relay and sending unit with a direct wire to the fuel pump. Is there anyone who has done this before who could offer some advice? Any guidance would be greatly appreciated.

Offline tyekid

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ECM-B fuse keeps blowing - 1991 Suburban
« Reply #1 on: April 06, 2021, 05:13:53 PM »
Hey everyone,

This past summer, I purchased a Forestry Service '91 Suburban. The past owner had mentioned fuel pump issues, so the shop I bought it from had already replaced the fuel pump. For a while, everything was going pretty smoothly. I even took the truck on a 1,000+ mile road trip down and back up the West coast without issues.

Right after I got back, I took my truck to work. When I went to leave, the engine would turn over but not start. The fuel pump did not seem to be getting any power. The ECM-B fuse had been blown, and any replacement fuses would immediately be blown when I began to turn over the engine. I ended up replacing the fuel pump relay and the oil pressure sending unit, which seemed to fix the problem.

A couple of weeks ago, I was on my way to visit a friend's house. I hit a speed bump a little harder than usual, and I immediately lost power. My ECM-B fuse had blown again. Currently, the replacement fuse is working, but I'm afraid to drive the truck anywhere before this issue is resolved.

At this point, I am mostly interested in bypassing the relay and sending unit with a direct wire to the fuel pump. Is there anyone who has done this before who could offer some advice? Any guidance would be greatly appreciated.

Offline Mike81K10

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Re: ECM-B fuse keeps blowing - 1991 SUburban
« Reply #2 on: April 06, 2021, 07:39:29 PM »
You have a short of course as is indicated by the fuse blowing when you hit a speed bump. Use an ohm meter to track it down. You can also look at the wire harness everywhere there is a chance of it shorting out. Some others on the forum may be able to provide further info. However, you will need wiring diagrams for your 91 and I believe the diagrams on the forum will be for 73-87 trucks.

Offline VileZambonie

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Re: ECM-B fuse keeps blowing - 1991 SUburban
« Reply #3 on: April 07, 2021, 02:48:39 PM »
Bypassing the ECM control of the fuel system is a terrible idea. Be thankful that the fuse is blowing and protecting your truck.

It's a pretty simple circuit and you can inspect everything visually first to look for obvious issues. If going over a bump causes the fuse to blow, then it would indicate you have a wire chaffed somewhere. Go to the obvious places first and visually inspect. At or around the oil pressure switch, fuel pump, along the frame rail, at the ECM etc.

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