Bad fuel pump or something else? **Solved**

[02Z71Raven]

I'll try to attach a video, but basically it turns over and then immediately dies. I put a gauge on the fuel rail and read zero pressure until you turn the key, then it goes to 50psi and then when it dies, it immediately drops back down to zero.
I thought I had just ran out of gas, but I put about 3 gallons or more in it and I do get some out of the gauge during that short moment of pressure.

System says the video files are too big. I'll try to size them downa bit and post em.

 

[OR VietVet]

Not holding pressure when off. Sounds like needs a fuel pump and always do the fuel filter at the same time.

But: Make sure, if you do replace the pump, that you check the pressure regulator as well. I was gonna look up but you did not share whether is flex fuel or gas and as of now, I am tired of guessing with no vehicle/engine info.

 

[02Z71Raven]

Not holding pressure when off. Sounds like needs a fuel pump and always do the fuel filter at the same time.

But: Make sure, if you do replace the pump, that you check the pressure regulator as well. I was gonna look up but you did not share whether is flex fuel or gas and as of now, I am tired of guessing with no vehicle/engine info.

Didnt realize it mattered when it came to the pump, so I apologize. It's a VIN Z flex fuel.
I replaced the pump a few years ago and the fuel filter just a couple thousand miles or less ago when troubleshooting another problem. I'll swap the regulator just because I haven't done it yet, if it has one.
I assumed fuel pump was bad because I ran low on gas and was parked for a while on an incline. I think I ran it too long on E.
At least I don't have a full tank

 

[02Z71Raven]

Any recommendations on a pump only?

My assembly probably has less than 5k miles on it. Don't really need to replace the whole thing.

Thanks in advance.

Edit: correction... My pump and assembly was replaced during recent troubleshooting also. So the whole thing has less than 2k miles on it.

 

[OR VietVet]

IMO, it needs to be diagnosed and then determine what is needed. You have some loaded statements. First: Yes it makes a difference if the 8th digit is a Z or a T, meaning gas engine and a different pump. Second: Replaced pump "a few years ago", meaning 3 years, 6 years...how many years and miles and what brand of pump. If it is relatively newer and a crappy brand, that can explain a lot. Don't cheap out and try just the pump, if you can find one. Do not assume the filter is still good, replace it with the pump:

More Information for ACDELCO MU2294

More Information for GM GENUINE GF847

More Information for GM GENUINE 2171582

BUT: I am still not convinced it is the pump unless you have a habit of damaging the pump yourself by running around close to empty all the time.

Being parked on an incline likely has nothing to do with it but I have been wrong before.

Do you trust yourself with the diagnostics or do you have a shop you trust?

Sounds like your existing pump is pushing pressure to the throttle body when the key is on and then dies because the pump just stops right then, when you release after the start. May have two problems: Pump and maybe ignition switch problem: Three choices of switch to pick from at RA.

to know for sure, you need to know if when it starts and release key and dies, does it still have spark, fuel pressure at zero or loses everything thru switch.

Hopefully others will chime in.

 

[Fless]

Flex pump for 2002 is AC Delco (Gold) MU2294 or DELPHI FG0810 (which might be OE). I replaced mine in my '04 a little less than 2 years ago and now the gasket is leaking and the evap test fails. I'll be pulling down my tank in the next few weeks to replace the gasket and lock ring and make sure it's well installed.

Don't know if we messed up something when we did it, but it was good for 22 months. I suspect that the bad canister vent valve didn't open when the ignition was off and allowed the tank to build up some natural pressure, maybe compromising the fuel pump gasket. Just a guess for now.

 

[02Z71Raven]

IMO, it needs to be diagnosed and then determine what is needed. You have some loaded statements. First: Yes it makes a difference if the 8th digit is a Z or a T, meaning gas engine and a different pump. Second: Replaced pump "a few years ago", meaning 3 years, 6 years...how many years and miles and what brand of pump. If it is relatively newer and a crappy brand, that can explain a lot. Don't cheap out and try just the pump, if you can find one. Do not assume the filter is still good, replace it with the pump:

More Information for ACDELCO MU2294

More Information for GM GENUINE GF847

More Information for GM GENUINE 2171582

BUT: I am still not convinced it is the pump unless you have a habit of damaging the pump yourself by running around close to empty all the time.

Being parked on an incline likely has nothing to do with it but I have been wrong before.

Do you trust yourself with the diagnostics or do you have a shop you trust?

Sounds like your existing pump is pushing pressure to the throttle body when the key is on and then dies because the pump just stops right then, when you release after the start. May have two problems: Pump and maybe ignition switch problem: Three choices of switch to pick from at RA.

to know for sure, you need to know if when it starts and release key and dies, does it still have spark, fuel pressure at zero or loses everything thru switch.

Hopefully others will chime in.

Yeah, the more I think about it, the more I question the pump as the culprit. It primes when the key is in the on position to a solid 50psi. Truck starts, then dies and pressure drops to zero. Makes me think that something isn't telling the pump to turn back on. Could be that I have to let go of the key, pulling it out of the start position and back into the on position.

Try again and it primes up and starts again, the immediately dies.

I've been troubleshooting electronics for 15 years, so I'm confident in my ability to test and troubleshoot, I just don't know what to test next.

Battery is on the charger so I'll try some other things tomorrow.

 

[02Z71Raven]

I can't remember the brand but I think it was a Delphi also that I bought at auto zone like 5 years ago. It had a lifetime warranty, so when I was doing some troubleshooting recently and it was in question, I just swapped it out under warranty.

 

[OR VietVet]

Delphi is a great brand and like @Fless, may have been OE supplier.

 

[02Z71Raven]

Things I noticed today while poking around.
0 psi on fuel gauge. Turn key to on position, get 50-52psi for 2 seconds then drops immediately to 0psi. Truck tries to start for 1/2 second turnover then dies (just enough spark, fuel and air to fire some cylinders). Fuel pressure stays up at 50psi while key is turning, then 2 seconds after it died, it immediately drops to 0. To be clear, when I say immediately, I mean immediately, not a slow drain, the needles sinks to 0psi in a flash.
My wireless remotes no longer work. The ability to turn the auto headlights on and off no longer works, it won't change states. When I turn the hazard lights on, the lights on my climate control, 4x4 switch and headlight control switch all flash in unison with the hazards. I don't recall ever seeing that before.
I've inspected quite a bit of the connections around all of these areas including fuse panels and bcm and under hood and it all looks to be in good condition. No corrosion, nothing unplugged.