2008 5.3 FF hard starting issue

[mxking1712]

Battery 3 years old. Tested with another battery last night no change. There is no fuel pump relay in this truck. 20 amp fuse under the hood and then down to the fpcm. I have 11 Volts at the module, 11 bolts on signal wire coming from ignition. But after the module there’s no real way to check without pulling tank down again. I wish someone knew the answer to my question. When the fuel pressure is below 58psi why doesn’t the pump run. In my mind if I shut vehicle off abd fuel pressure is above 58 sure the pump won’t run. But after sitting and losing some pressure pump won’t run again. Sometimes it does sometimes it doesn’t. I checked the two grounds(one at module and one by the pump) both checked good. If someone actually knows how the fpcm and ecm work together that could explain it to me, that would be greatly appreciated

 

[mxking1712]

I should also add, I did some research on these injectors and the oil sending unit. The way I understand it, when you turn key on, fpcm sends a signal to prime fuel system. Once that is done, engine cranking starts to bring oil pressure up and this is what keeps pump running continuous is that oil pressure signal.
This almost makes sense with my problems, with fuel pressure around 30psi for example, my pump won’t run, engine starts to crank and injectors don’t open(sounds like they won’t open with less than 50psi initially) once oil pressure starts to come up under engine cranking, fuel pump kicks in, and it starts up.

 

[wsteele]

I should also add, I did some research on these injectors and the oil sending unit. The way I understand it, when you turn key on, fpcm sends a signal to prime fuel system. Once that is done, engine cranking starts to bring oil pressure up and this is what keeps pump running continuous is that oil pressure signal.
This almost makes sense with my problems, with fuel pressure around 30psi for example, my pump won’t run, engine starts to crank and injectors don’t open(sounds like they won’t open with less than 50psi initially) once oil pressure starts to come up under engine cranking, fuel pump kicks in, and it starts up.

I think you lost me.

I will be honest, it is really hard to stay in here with you. In your first post you said you changed the fuel pressure regulator on the fuel rail, but your truck doesn't have a fuel pressure regulator on the fuel rail. Then in that same post you said you swapped the fuel pump relay, but your truck doesn't have a fuel pump relay.

The symptoms you describe pretty much land on either the FPCM or the Fuel Pump (which has the fuel pressure regulator in its main assembly), so the two most likely candidates have been replaced.

The only thing I can offer is maybe one of the two components that likely are your problem, when replaced, were not functional. But I will say, it is pretty long odds that the new unit (either FPCM or Fuel Pump) was DOA in the exact same symptom you replaced it for.

The only other thing that is in the mix (from my perspective) is the fuel pressure sensor. I guess it is possible that it is reporting in error, but that is easy to check. Just go down to NAPA and rent a fuel pressure gauge. The rental actually is free, they just charge your card in case you don't return it. After returning it, they credit your account in full. It will take about 5 minutes to verify your pressure sensor is good or bad, using the analog gauge and your ODB scanner.

Good luck.

 

[mxking1712]

I will admit I was a bit confused when I first started this thread, I had done some trouble shooting a few months ago, and stopped. When I made the post I had somewhat forgot what I had all done.
When I said fuel pressure regulator I meant purge solenoid on the fuel rail. My mistake.
And onto the relays, I also did not understand about the module until I made this post. I thought the fuel pump ran off the run/crank relay. I have re read what I have posted here the first few posts and I agree with you it would be confusing.
I’m sorry for that.
I appreciate the advice I have gotten so far, it has gotten me to check more stuff and more importantly learn more.
I have a fuel pressure gauge on order to compare with the sensor.
If no one else has any ideas that’s alright, I will eventually figure this out. I don’t like leaving things like this unresolved. Thanks for your help

 

[Edgar1740]

Did you end up finding the issue I have the same problem on my 2008 Silverado 4x4 5.3

 

[Fless]

Did you end up finding the issue I have the same problem on my 2008 Silverado 4x4 5.3

Well, the OP hasn't been here in two whole years, so I wouldn't expect an answer. Might want to consider starting your own thread with some details about your rig, what's been done to it, and the specific symptoms it's experiencing.