No fuel

[GarmrYuk]

I have a 99 Yuk 5.7L This thing fires up like the day it left the lot. But recently as I pulled out out my driveway it died. Instantly. No sputtering. Just dead. My fuel pump wasnt running. I checked the relay. Good. Signal to 30 86 and 87. Good. 85 intermittent. It runs to the pcm. I changed the oil pressure sensor switch. It must have been bad for a while. Years probably. Now it runs and stays running when I trick it into starting. But it still does not start. Fuel pump is 5 years old. I thought about ignition switch but everything else seems to work with it. I have taken it to 2 different mechanics neither could figure it out. One is a GM mechanic who went on his own 10+ years ago and it very reputable. Sometimes it will start after several short cranks. The oil pressure guage climbs up ever so slightly after a few cranks and bam! It's running. This is without any prime from the ecm. There is also no return from the pump when I shut it off. Anyone know what this could be. Thanks

 

[Schurkey]

Does the pump prime when you turn the key? If not, the computer isn't controlling the fuel pump relay properly. Broken/corroded wire, failed ECM.

I don't know what you mean by "no return from the pump when I shut it off." When you shut it off, the fuel pump stops pumping, There wouldn't be any "return" when there's no supply.

 

[GarmrYuk]

Does the pump prime when you turn the key? If not, the computer isn't controlling the fuel pump relay properly. Broken/corroded wire, failed ECM.

I don't know what you mean by "no return from the pump when I shut it off." When you shut it off, the fuel pump stops pumping, There wouldn't be any "return" when there's no supply.

The pump doesnt prime when I turn the key. Under normal circumstances if you turn the key on it should prime. Let it finish priming and turn the key off and it should run the pump again but I think for not as long. This is something that the ecm does by signaling the 85 pin on the fuel pump relay. I assumed that it was doing something like an unprime but idk for sure why they do this. I bought a new ignition switch and I will put it in and I will try to replace the wire running from the ecm to the 85 terminal on the fuel pump relay. If that doesnt work I will borrow a known good ecm and try it. Thank you.

 

[Schurkey]

The pump doesnt prime when I turn the key. Under normal circumstances if you turn the key on it should prime.

Yes. Failure to prime is a genuine concern.

Let it finish priming and turn the key off and it should run the pump again but I think for not as long. This is something that the ecm does by signaling the 85 pin on the fuel pump relay. I assumed that it was doing something like an unprime but idk for sure why they do this.

The fuel pump does not run with the key "off". There is no "un-prime".

I bought a new ignition switch and I will put it in and I will try to replace the wire running from the ecm to the 85 terminal on the fuel pump relay. If that doesnt work I will borrow a known good ecm and try it. Thank you.

I'd test the wire from ECM to fuel pump relay 85 rather than just replacing it.
I'd verify proper voltage to the ECM inputs rather than just replacing the igntion switch.

If everything tests good, but the ECM won't prime the pump...yes, you might need a different ECM. Perhaps the fuel pump relay driver failed.

 

[GarmrYuk]

The fuel pump does not run with the key "off". There is no "un-prime".

Huh? That is strange. Since I have owned this thing it has ran the fuel pump for a few seconds when I switch the key to the off position. I also have seen this with a test light on the 85 pin when the ecm decides to communicate. Im not arguing. I am just saying what I know that mine has been doing. Do you know what would cause this?

 

[PlayingWithTBI]

Huh? That is strange. Since I have owned this thing it has ran the fuel pump for a few seconds when I switch the key to the off position. I also have seen this with a test light on the 85 pin when the ecm decides to communicate. Im not arguing. I am just saying what I know that mine has been doing. Do you know what would cause this?

Maybe you have the hot fuel module?

 

[Schurkey]

More likely, it just takes a few seconds to drop the oil pressure; so the oil pressure switch keeps the pump running.

But I would have expected that with the key "off", there'd be no connection to battery power. I'm somewhat surprised the pump runs with the key "off".

No matter what, there is no "un-prime". The fuel system should be holding pressure.

 

[Supercharged111]

The pump in my 1500 has always done this. I've long wondered if it was a relay sticking, but it's fed by ignition power isn't it? Usually just a second or 2, but on a couple occasions it's gone a solid 5 seconds after turning the key off. This was with both the factory blackbox PCM and also with the newer LS based 411 that's in there now. I'm pretty sure the Vortecs didn't get the pump controlled by the oil pressure switch?

 

[GarmrYuk]

Maybe you have the hot fuel module?

I looked up what a hot fuel module is and it describes what my Yukon does perfectly. Thank you.

 

[GarmrYuk]

The pump in my 1500 has always done this. I've long wondered if it was a relay sticking, but it's fed by ignition power isn't it? Usually just a second or 2, but on a couple occasions it's gone a solid 5 seconds after turning the key off. This was with both the factory blackbox PCM and also with the newer LS based 411 that's in there now. I'm pretty sure the Vortecs didn't get the pump controlled by the oil pressure switch?

Playing with TBI just mentioned a hot fuel module. Look that up and read a description of what it does. Based on my research it would not matter what pcm you have. It overrides the pcm and runs the fuel pump after shut off to keep the fuel cool as temperatures rise under the hood. I suppose that with manual fans this makes sense. You shut off the motor and you shut off the fan.