05 5.4L I couldn't get my truck to start the other day, scanner showed no fuel rail pressure, jumped the fuel pump to make sure it was working. worked fine. Hooked the fuel line back up and jumped the pump again to get fuel into the rail. Again KOEO showed no fuel pressure. But it did start. Once running I had 30 psi. let it run for 10 min and it stayed at 30 psi. shut it off for 10 min. Went to start it again and it showed no fuel pressure but it did start again though it took a few seconds. Shut it off for 20 min. Went to start it and again KOEO no fuel pressure. this time it took awhile to start, about 20 seconds. but again once started it stays at 30 psi.
So the longer I let it sit with the engine off the longer it takes to start.
So driving down the road with barely any throttle it stays at 30 psi, once I give it gas it drops below 20. if I really give it gas the pressure will drop below 15 or 10 psi. of course the truck picks up slowly as the pressure increases.

 

There is a fuel module that controls the pressure and starts the pump. They are known to go bad. This is a small 2 x 3 inch box , and inch thick, mounted on frame above the rear axle, drivers side, about half way between the tire and the pumpkin. Should have a small wire harness to it. Take it off and see if it is corroded on the backside.

 

 

Hey thanks for the reply. I have already changed the FPDM as well as the fuel pump and fuel pressure sensor.

 

are you saying you installed a new pump and module and that fixed it, or you had previously changed them and now you have a pressure problem ? The module and pump are about all that controls the system, besides a few feet of wire and a fuse.

 

Well I replaced all of those when the truck wouldn't start a few months ago but then found the power wire to the FPDM was corroded at the plug under the drivers door. I didn't find the wire until after I replaced everything.
I guess ever since I bought the truck it has had this problem of low fuel pressure but I just didn't really realize it until I started digging into the truck. I would have saved some money but you live and learn.
After much research and reading and asking and testing I decided it would be best to take to a mechanic. I hate paying someone to do something because no one takes pride in their work they just want to get paid but I have no choice now I need the truck running right. I don't have enough knowledge in electrical to pinpoint the problem.


Thanks for all the help!!!!!