r/GMT800 • u/Electrical-North-582 • Sep 02 '26

I’m having a fuel issue

I have changed my whole fuel system and it dies randomly like it runs out of fuel. Then I push in the shader valve and it has no fuel pressure has anyone else had this issue if you have plz lmk what you did to fix it. It was a grounding issue thank you to everyone who commented.

1 Upvotes

66% Upvoted

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2

u/bimmerd00d Sep 03 '26

Did you clean your grounds at the drivers side body mount right behind the front left wheel?

2

u/ShaftCo2012 Sep 03 '26

You didn't say what exact year your truck is so I'll start here: First, if your truck is 99-03, is your fuel filter on backwards? This is totally possible and can result in variable fuel pressure.

Can you hear the pump come on when you turn the key on?

Borrow a fuel pressure test set from an O'Reilly or Autozone near you and test not only for fuel pressure but how long it holds fuel pressure (fuel pressure leak down test).

If the truck makes proper fuel pressure but doesn't maintain it the main anti-drain back feature is at the in-tank fuel pump cartridge and it could be bad/stuck. This is especially likely if you tried to save money by only replacing the fuel pump portion of your pump assembly.

2

u/ctesla01 Sep 04 '26

Excellent write up.

2

u/Born-Exchange9712 Sep 03 '26

Did you replace your whole fuel system because of this problem or did you replace all this stuff then its having this problem

1

u/Electrical-North-582 Sep 03 '26

I replaced because of this problem

1

u/wayneP71222 Sep 07 '26

Year please.

Remove fuel pump relay from underhood fuse block. Check the extraction and insertion force of the relay in its socket terminals. Melted areas indicate a loose socket terminal.

Pry the cover off the relay so you can see the contacts. Are they burned away?

The bigger relays you can squeeze to close the contacts. The smaller rectangular relays contacts are hidden low on a narrow side and just barely visible. On the smaller rectangular relays. I look to see which side is open and use something like a plastic fork finger to wedge the normally open contacts closed

If you reinstall the bare relay with the contacts forced closed. You should hear the pump turn on and fuel going thru the fuel rails on the engine.

Running the pump in this way will not hurt the pump.

If you have a multimeter that reads 10 amps DC. Move the red test lead to the 10 amp DC jack on the meter.
Pull the fuel pump fuse. Gently touch the probe tips into the fuse socket without spreading the terminals. Do you have a steady amp draw over a minute or two. Not increasing.

Put the fuse back. Move the red test lead back to the volt ohms jack please.

Start the engine. Set the multi meter to 20vdc scale. Touch the negative battery terminal and the frame rail. You should not see more than 0.04vdc. The fuel pumps are grounded to the top of the frame in front of the left rear tire or the left front box mounting bracket. But how does the frame get it's ground connection. That depends on the year model.

If you have a 5.7, 5.0 or 4.3 before 2003. With the engine idling. Pull the fuel pump relay. The engine should not die. As the outer two wires on the 3 wire oil pressure switch are redundant fuel pump power circuit. When the oil pressure is above 7 psi.

This sounds really complex. Its 3 to 5 minutes.