In a real pickle with fuel pump issues. Advice appreciated!!

[jj3393]

EDIT: SPRAYING STARTING FLUID IN THE THROTTLE BODY GETS IT TO CRANK FOR A FEW SECONDS.

This is for a 2004 GMC Yukon 5.3 (Flex fuel). Working on what was thought to be a bad fuel pump. Vehicle was purchased, then driven 120+ miles to destination. It was parked then not touched again until now. Sat for a couple weeks. After all the ok driving and no issues, now it won't start. Diagnosed (from others) as a bad fuel pump. Have been through 3 brands of pumps, and no matter what none of them will prime or turn on at all. Have checked female adapter multiple times. Getting around 12V. Relay is good. Ground seems to be good. Everything has power until hooked up. Nothing is working. It's becoming a headache. Anyone else with this issue? Also, sometimes it will turn over and start to run then dies immediately (fuel pump still doesn't cut on)

 

[S33k3r]

Sounds like a security lockout. Might look for a kill switch somewhere. And, as always, a code reader might help (it might not, though). Also, the wiring at the gas tank it self could be causing an open in your circuit. Did you replace all the wiring at the gas tank?

 

[jj3393]

We have a computer to check. When we try to start it the immobilizer symbol comes on for a second then off, but unsure of the security part. We've asked if it got messed with. The answer was no, but it's funny that it ran perfect before. A long trip at that. Then one day it just didn't crank. I have no clue where this switch would be..

 

[Fless]

Does it always turn over (crank)?

If so, start simple. You can rent a fuel pressure test kit at just about any name brand auto parts store and test the key on, engine off fuel pressure. Alternately you can also do a simple test at the same schrader valve on the passenger fuel rail with a rag and a small screwdriver. Put the rag over the valve and depress the valve (it's like a bicycle tire valve, but larger) and see if the fuel shoots out or just dribbles.

If the fuel pump does not turn on for a second when the key is turned on (not cranked) then you might swap the fuel pump relay with another one that is the same (some of the others in the underhood fusebox are identical).

 

[George B]

How are you determining the pump isn’t priming? Pressure gauge?
Can you force the pump on with the fuel prime terminal under the hood of it has one?

 

[jj3393]

Actually have done all that as well. Even with the original pump, there was no pressure period. Though the new one is in there it seems that none of these pumps are getting power once connected. They harness (male) reads 12V

 

[jj3393]

How are you determining the pump isn’t priming? Pressure gauge?
Can you force the pump on with the fuel prime terminal under the hood of it has one?

There's two of us. The sound is prominent obviously once the key is turned over. We've both been beside the pump during the "attempts to crank" and not even a whisper of a sound.

 

[Fless]

For your voltage measurement are you reading the ground on the connector, or using a chassis ground for your VOM connector? Must use the connector ground.

Swapped the fuel pump relay with another as a test? Pick another identical one and swap it in the fusebox. EDIT The DRL relay right next to the fuel pump relay is the same; could swap those two.

 

[Fless]

So you're saying the pump primes with the key on before you crank it, but the pump doesn't run when it's being cranked?

If that's true and the pump primes with key on, what kind of pressure is at the fuel rail (without cranking it)?

If you have jumper cables connect to battery negative and to the GROUND connection on the alternator bracket; that will test for a good engine ground. You could also move that test connection to one on the body at the firewall, but I'm not sure body ground is an issue.

 

[jj3393]

We have swapped relays. All are in good working condition. Nothing of this makes sense. Like I mentioned, everything has power. Relays, harnesses, ect. Primary problem is basically the power to the pump disappears once connected to the power supply harnesses.

 

[jj3393]

So you're saying the pump primes with the key on before you crank it, but the pump doesn't run when it's being cranked?

If that's true and the pump primes with key on, what kind of pressure is at the fuel rail (without cranking it)?

If you have jumper cables connect to battery negative and to the GROUND connection on the alternator bracket; that will test for a good engine ground. You could also move that test connection to one on the body at the firewall, but I'm not sure body ground is an issue.

No. The pump won't turn on or prime at all during any of this. Also, using the connector ground during testing.

 

[Fless]

Just out of curiosity have you checked the PCM-B fuse that is next to the fuel pump relay? Pull it out and make sure both legs are intact and it's not blown and has good tension on the blades.

 

[jj3393]

The 20A? Yes

 

[Fless]

Have you tried banging on the underside of the tank while the truck is being cranked?

 

[Fless]

The only other thing I can think of would be wiggling the ignition cylinder somewhat as you turn the key. Pick up on the key cylinder a little in case it's worn. Other than that, checking the voltage on both sides of all critical fuses like for the BCM (the inside left panel fusebox holds at least 3 TBC fuses).

 

[jj3393]

Have you tried banging on the underside of the tank while the truck is being cranked?

Haven't done this. We are also only hooking up connections while fuel pump is out of tank. The tank is dropped, but we removed the pump from the tank itself while testing harness connectors

 

[iamdub]

I'm understanding this as you have 12V and ground at the vehicle harness (unplugged from pump's connector) for a few seconds when you turn the key on (priming). But, you don't get voltage when it's plugged into the pump's connector and turn the key on again to prime. If you unplug it and check for voltage again, it's there. Is this correct?

Do you get 12V and ground when cranking (still unplugged) ?

Screwy things happen with low voltage. After it sat for those few weeks, was the battery low when you first went to start it?

With the pump installed (any of them) and the tank in place, did you connect the ground on the filler neck to the body?

 

[jj3393]

The amperage goes down when trying to crank. Also did not connect filler neck during any of this. It's primarily just trying to get power to the pump once connected. The harness' have power, but once you plug the pump up, it doesn't power the pump itself

 

[Joseph Garcia]

Welcome to the Forum from NH.

Lots of knowledgeable folks here who freely share their knowledge, experiences, and perspectives. Knowledge is power.

I hope that you will become a participating member in the Forum's discussions.

Pics of the truck, please.

You are already receiving sage advice from the knowledgeable folks on this Forum. They will help get you through this issue.

 

[Mudsport96]

Ok so how did you determine power at the connector?
Did you probe the connection from the back side or did you push the meter leads into the pin side of the harness?

If you did the front side, it is possible that you spread the terminals enough that they dont make contact with the pins on the pump side of the connector.
Second, if you have the clamp style meter, pull the wires out of the loom enough to get the amp clamp around the positive wire. Then key on to see how many amps are being drawn. I have seen 12v at the pump but corrosion in the harness caused an amp drop not allowing the pump to actually run on one of my own vehicles.