Bad fuel Pump? (Solved)

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WestCoastie

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(Edit) Solved, new fuel pump fixed the issue.

(Edit… to the Edit) A week went by of normal starting. Then the hard start acted up again. Only thing I hadn’t replaced is the cam sensor, it tested ok. Replaced it with GM genuine cam sensor and no more problems.


2003 GMC Yukon XL 1500 5.3

Back Story:

1. Engine spun a bearing
2. Sat outside for 6 months or so before got around to rebuild
3. After rebuild experienced hard starts (would sometimes fire right up, other times I had to crank a couple times before it finally would start up). But once it was running it seemed to run just fine.

I chocked up the issue to an electrical gremlin. As I had a couple to figure out after truck sat for so long. Eventually I fixed everything besides the hard starting (and 4x4, but that’s a whole other issue).

A week ago (right before heavy snow started falling) the truck just refused to start altogether.

Finally got a test kit to measure fuel pressure. When I initially put it on there was no pressure. I jumped the fuel pump and got up to about 50psi. After removing power, pressure fell to about 40 and slowly started falling.

I only jumped the fuel pump relay because it was easier, not because the key won’t activate it.

Everything about this screams fuel pump to me. But the fuel pump was replaced at 30k miles (about 110k in it now).

Im curious what everyone thinks.

Thanks!
 
Last edited:

Trey Hardy

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2003 GMC Yukon XL 1500 5.3

Back Story:

1. Engine spun a bearing
2. Sat outside for 6 months or so before got around to rebuild
3. After rebuild experienced hard starts (would sometimes fire right up, other times I had to crank a couple times before it finally would start up). But once it was running it seemed to run just fine.

I chocked up the issue to an electrical gremlin. As I had a couple to figure out after truck sat for so long. Eventually I fixed everything besides the hard starting (and 4x4, but that’s a whole other issue).

A week ago (right before heavy snow started falling) the truck just refused to start altogether.

Finally got a test kit to measure fuel pressure. When I initially put it on there was no pressure. I jumped the fuel pump and got up to about 50psi. After removing power, pressure fell to about 40 and slowly started falling.

I only jumped the fuel pump relay because it was easier, not because the key won’t activate it.

Everything about this screams fuel pump to me. But the fuel pump was replaced at 30k miles (about 110k in it now).

Im curious what everyone thinks.

Thanks!
Sounds like the pump to me. No fuses blown correct?
 
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WestCoastie

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Sounds like bleeding off fuel pressure and that could be the fuel pump or injector(s) or line leak or.....etc.
I dont see any signs of leaking outside the system. Nothing coming out exhaust as if flooding from leaky injector(s). I figure if injectors were leaking I would still at least get a bit of a start.
 

Trey Hardy

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Correct none blown, and due to other electrical issues almost all grounds have been found and cleaned up
If you don’t know for sure it was a quality pump I’d put a good one in there personally but it could be as simple as a relay?
I said that about the fuses cause a buddy of mine went to some new shop to have his fuel pump fixed and it still wouldn’t run… come to find out the fuse was blown lol but now since he cheaped out on the fuel pump the gauge don’t work anymore so he’s got to go back into it again to get that straight or put the stock pump back in the truck
 

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See the post below for specific fuel pressure test and specs. Replace the fuel pump relay just to rule it out; maybe test with the old one and again with a new one.

The Flex Fuel system on your year will have an inline fuel filter on the driver's side frame rail (near the alcohol sensor); consider replacing it if the age is unknown.

 
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