Fuel pump unit replacement

Tiny
SAMFGR
  • MEMBER
  • 1999 GMC SIERRA
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
I've noticed after I replaced the fuel pump and fuel filter my truck was still cutting off after every start. I checked all the fuses and the fuel relay. When I replaced the 20amp fuse the fuel relay did click for a second or two after that I decided to start the engine and for 10 plus seconds was running fine. Then I went to check the fuel pump was running. All of a sudden I saw right before my eyes that the wiring connected to the fuel pump wiring hardness before the connector started to heat up in smoke. Then the engine started to sputter. Question? Why or what made the wire harness to short out the way it did? Started to burn? I'm very concern. Can anyone explain?
Monday, August 9th, 2021 AT 10:07 PM

4 Replies

Tiny
SAMFGR
  • MEMBER
  • 2 POSTS
Just fix it. Praise Jah. Undo the wire harness right before the fuel pump connector, and found out one of the wires was spline. Must have short out. Wrap each one with electrical tape and douse it with electrical paste. Working like a charm. Had to douse myself with a 12 pack, extremely happy camper. Hope this works out for anyone out there.
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Tuesday, August 10th, 2021 AT 12:47 PM
Tiny
MASTER ASE TECH
  • MECHANIC
  • 82 POSTS
Glad you found the concern and repaired it.
Dan
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Wednesday, August 11th, 2021 AT 11:55 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Good job in finding it.

Basically the wires shorting like this and starting to smoke is due to a rub through in a harness so that the wire is touching straight to ground. Basically the electrical circuit needs a load on it otherwise it is like opening flood gate electricity. By having a load there like the fuel pump it actually uses the voltage and turns it into energy and keeps the circuit intact.

So a short normally shows up by smoking wires.

Here are a couple guides that will help others in the future to try and find this before they find the smoke:

https://www.2carpros.com/articles/how-to-check-wiring

https://www.2carpros.com/articles/how-a-car-electrical-system-works

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

I am attaching the wiring diagram as well which will help with this testing.

I would suggest cutting out any damaged wires and splicing in new sections of wires just to be sure this doesn't happen again. When they overheat like this, they do tend to get brittle and will cause more issues in the future.

Lastly just in case others search this in the future, I am providing the process for replacing the pump as they may be looking for this based on this title.

Thanks for updating us.
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Wednesday, August 11th, 2021 AT 12:11 PM
Tiny
SQM
  • MECHANIC
  • 6,383 POSTS
Hello,

It's great that you figured it out.
As you have found it, wires can heat up and smoke if there is break in the insulation and two un-insulated wires touch crating a short. Which will blow fuses.
Do appreciate you sharing your solution with us.

Thank you!

https://www.youtube.com/c/2carpros/featured
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Wednesday, August 11th, 2021 AT 12:31 PM

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