Keep losing fuel pressure...can’t figure it out

[BKK]

Hello all, I’m having quite the problem with my truck. Ever since I replaced the intake manifold gasket, oil pressure and cam sensor I’ve been having an intermittent hard start problem. Sometimes it will just crank until I turn the key off and back on, then it starts fine. It runs great after it starts up.

 

So far I’ve tried replacing the fuel pressure regulator, that didn’t help so I was convinced it was the fuel pump. Swapped in a Delphi unit last night and it’s still having the same problems. I was frustrated so I pulled the fuel rail off with the injectors and primed the system and none of the injectors were leaking fuel.

 

With a fuel pressure gauge hooked up the pressure drops to about 10 in a few minutes and then slowly to 0 after that. Sometimes when i turn the key on it will instantly shoot to 50psi and start right up and other times it will need a couple key cycles to start...I don’t understand what’s going on.

 

if it’s not the fuel pump, fpr, or injectors then what else am I missing? No leaks anywhere that I can see...

[BKK]

I was just messing with it and the pressure goes up and down when I squeeze the supply line with vice grips, but nothing changes when I squeeze the return. Could it be sucking in air around the injectors?

[Mike GMC]

If squeezing the pressure line makes changes and no the return, it could be that there is a pressure leak after the pump but still in the tank.  That is unless you see fuel on the floor.  This could be the cause of the rapid bleed down you see once the key is off.

[riverbanks]

When you said,it needs a couple of key cycles to start up,are you hearing pump running each time?

[BKK]

33 minutes ago, riverbanks said:

When you said,it needs a couple of key cycles to start up,are you hearing pump running each time?

The previous pump was way louder, the new Delphi one I put in is a lot quieter but still builds pressure the same.

[BKK]

1 hour ago, Mike GMC said:

If squeezing the pressure line makes changes and no the return, it could be that there is a pressure leak after the pump but still in the tank.  That is unless you see fuel on the floor.  This could be the cause of the rapid bleed down you see once the key is off.

It’s weird though because when I completely crimp the line off it still leaks pressure fast, unless I’m not completely closing the line down then it makes me think it’s something with the fuel rail or injectors. When I put the new pump in it came with the big rubber seal.

[usmcdevildog73]

On 4/12/2020 at 1:21 PM, BKK said:

It’s weird though because when I completely crimp the line off it still leaks pressure fast, unless I’m not completely closing the line down then it makes me think it’s something with the fuel rail or injectors. When I put the new pump in it came with the big rubber seal.

Hi BKK.  Did you ever figure out what was going on? I have the same issue.  New pump etc.  My pressure doesnt drop off as fast as your s though.