04hdlariat

Fuel pressure runs right at or around 40psi.

yourwheelsarerolling

working on a 2004 f-150 5.4 and have 2 codes- P0191 & P1237. have replaced fuel filter, frp sensor (fuel rail pressure sensor), fpdm (fuel pressure driver module), and the fuel pump. all these parts have been replaced before upon inspection. codes have been cleared, ground for the fpdm has been relocated, all plugs were serviced with electric grease, and no vacuum leaks were found for the frp sensor. any suggestions on what could be the problem for these 2 codes to persist?

jackaz6K

im new to this and all forums this is my 1st post anywhere, so if i am breaking any kind of protocol please be gentle. ok like the original poster of this thread i have done alot of searching on this topic, with no good out come. i have a 2005 f150 lariat 5.4

i am no mechanic but i am mechanically inclined here is a quick summary:
new cats
new plugs
new coils
new fuel filter
new pump twice
new fpdm

i have had the plugs swapped(none broke according to mech)/tune up, oil change, fuel filter a month ago about a week later it seemed to lose power at about 2000rpm, it is drivable if i drive very light footed however passing it doesn't do to good. so i took it back to mechanic and he said tranny issues, not trusting i took it to another mechanic who said cats (i replaced) then said it was losing fuel pressure when driving and i needed a pump, they also said the cleaned the TB and MAF. so i installed a new pump no fix, then took it to another mechanic and he said pump as well and that i should get a motorcraft. i did not get a motorcraft pump i used the lifetime warranty on the Napa pump and still no fix. i tried a new fpdm still bad what next, i do have a Bluetooth scanner and torque unfortunately i dont understand most of it.

i will mention that during this process i did get misfire on #2 and #4 which turned out to be the coil plug which i soldered on new ones and no misfire and no code again. by the way this has been to 5 mechanics one being ford and still no luck, i really dont think ford even checked anything they wanted me to replace all 8 coils at 1000 dollars.

i dont have much more money to spend and i really need to drive my truck, any help anyone can give would be great.

i forgot to mention that when the pressure gauge was connected on fuel line at firewall the gauge stayed at 28psi and when engine was revved the pressure dropped signifcantly.

20064x4

I had a similar experience on my old 1979 dodge 4x4 back in the 80s. I bought a faulty fuel filter. I suggest getting another new filter and installing it.