So it often just cranks for 15 seconds before it fires. I put the fuel pressure guage on it and you turn the key on but don't engage the starter it goes to 30 psi then back to 0 in a 2 second time frame. It then stays at zero. when you engage the starter pressure slowly goes up and it starts running while running its a consistent 60 psi.
I presume its the fuel regulator but why does it not go up to 60 psi and why does it just stop with the KOEO?
Is it reasonable to just replace the regulator? or should I be replacing the fuel pump to at the same time? I will be doing this from under the truck since there is a lot of hard mounted equiptment in the bed.
Seeing as how its slow to come to pressure & then won't hold pressure after the engine or pump stops, it kinda sounds like the regulator check valve is on the fritz & maybe the pump is getting weak too???? With it being 9 years old & kinda a pia to get at & change out, I'd just opt to replace the entire pump/regulator/sender assy & call it a day.
fuel pressure port is on the back of fuel rail near the firewall, not super easy to use.
I have two 2003 4.0s that had the same problem it was one of the lines on the fuel pump assembly had pinholes in them allowing the fuel pressure to blead off and not stay steady. Probably could of just replaced the hose but went ahead and just replaced the fuel pump assemblys they start just fine now.