2001 gmc Jimmy 4.3l v6

***Replaced fuel pump

***checked fuel relay under hood- working fine (tried jumping the relay with paper clips, didn't work)

***Power IS getting all the way back to the wiring harness that connects to the fuel sending unit (receiving 10 volts)

***Cleaned up the ground well

I've test each of these multiple times, and the fuel pump still wont turn on. I hooked the fuel pump (via wires) to a car battery and the fuel pump started pumping out fuel right away. yet when its hooked up to my truck it wont turn on.
Anyone else had this problem? Suggestions? Are there any other relays/fuses I need to know about?

 

10 volts is not enough to power the pump like you said you ran power from the battery and it worked so that means you dont got enough power going to the pump


I say swap the relay and see if it starts working

Just pull the one next to it and replace it with the pump relay

 

Swapped it with the relay foe the horn (horn works) it still won't work...

 

Let's start with which wire on the connector you're getting 10 volts at.

Plug Pinout (courtesy of Swartlkk)

10V at the grey wire should be enough for prime. Once running, this voltage should increase. I agree though, that a 2+ voltage drop isn't a good thing....

EDIT: if your only getting 10 volts, it's possible that you're measuring one of the fuel level sending unit wires. (PPL or BLK w/WHT)

Try running a new ground from pin C - the BLK wire with no trace. If the pump lights up, you've found the problem.

If you don't have voltage on the grey (Pin B) of the connector, check that you have output at the relay, and go from there.


Keep us informed.



Aaron

 

@aneill75 The friend who was helping me work on my truck left, so I'm not sure when I'll be able to work on it again (sigh) The fuel sending unit they put in the jimmy's is different now Airtex Master/Fuel Pump (E3954M) | 2001 GMC Jimmy 4WD 6 Cylinders W 4.3L SFI | AutoZone.com
They changed the connector required.

Also after speaking with my friend (he was the one reading the wires, i was the one turning the key) he said that at first he was getting voltage, but then he wasn't sure if he was checking the correct one. So it may still be the wiring.

As soon as I know something/ can get to it. I'll keep you updated. Thanks

 

Verify the wiring is correct on the new connector. Has the truck run since the new connector was installed?

Get a wiring diagram for your year of truck and study it. Get some colored pencils and trace the entire circuit for the pump. It makes it much easier to troubleshoot.

 

Yes, the truck had run. I actually used it that morning, came home and parked it for about 1.5 hours then it wouldn't start. Still think it's wiring?

 

I am going to assume that your Jimmy was running before the fuel pump went. So, your wiring to the tank should be ok. I would verify that the *new* connector was, in fact, wired up properly

Truck used to run & fuel pump runs if directly connected to a battery.......me thinks we've found the problem.

Let us know once you've had a chance to look. The diagram posted above has the color code for the wires on the vehicle side.



Aaron

 

That's pretty important fact to know.

Check owner's manual and find inertia sw, bypass it. But the prime suspect is always any changes recently made.

Plus relays and fuses

 

I was reading my manual, and it also suggest then when having trouble diagnosing the fuel system. It could be oil pressure related .That if the oil pressure drops down to low, it will will act as a fuel pressure cut-of.

Would that make it so that I'm not getting anything back to the fuel pump?

Furthermore, how can I bipass the oil pressure sensor to test and see if that is it?

(I know oil pressure might not be so common, but hell... with this vehicle I really would not be surprised)

@pettyfog You are very correct, that is very important information. I've been so stressed recently with this truck and other stuff that it slipped my mind. I will try to not forget anything else for you guys.