fuel pressure too much

Hello , I have a 2004 F150 with 5.4 (3 ) valve. I joined this site to hopefully learn how to troubleshoot and repair somethings and not be totally dumb to some of the less than honest mechanical shops since i travel alot for my job makes it hard to find a good reliable and honest mechanic. with that being said after throwing a bunch of money and Time at this truck but only after I had a local shop charge me $2,300.00 at what I thought was a fuel pump , this is the list of what they said they replaced on it Fuel Pump,Fuel Pump Driver Mod. Fuel Injectors, New PCM .New Plugs , I had to call a Tow Truck to get the truck back its Pushing (91 psi } out and they said they cant get it down .So instead of thrown my money away I decided to try to fix it on my own And learn something in the process the wiring harness that the truck had on it was in bad shape so i recently purchased a new one and hopes of it correcting the problem i just wondering where some of you might start to trouble an issue like this I appreciate any help . J

Now that's a new one! :silly: Never seen that one before.

Can you give us an idea of what test equipment you have available to you? Test light, multimeter, scan tool, fuel pressure gauge? What you have available will help us decide what testing to suggest.

It's also important for us to know what testing you've done yourself. I don't mean what the shop did - I mean what YOU'VE done. It's important to start on your own diagnostic path, not just pick up where the shop left off.

If you haven't already familiarized yourself with this fuel system, I snipped this bit from the OBD Theory and Operation. I've highlighted (what I believe to be) the important part:





Does your truck have a P1235 stored? Because a fuel pump duty cycle of 100% would definitely account for your 91 PSI fuel pressure.

the ECT (engine coolant temp) sensor has a great deal to do with the proper operation of the fuel system in the Ford electronic return-less fuel system. if the engine does not reach 205 coolant temp, the PCM sees this as a cold engine and commands the fuel pump to stay on. If your having wiring problems this will affect the voltage outputs of various sensors. If it is interfering with the ECT sensor the proper voltage will not be reported to the PCM. at 205 degrees, voltage output should be about .55v. cold engine depends on ambient air temp but should be around 3v.

I really dislike parts changing mechanics...