Thats a BIG problem right there... Pressure should be 36-38 psi with vacuum to the FPR. When removed it should jump 5-6 psi. Do you see black smoke when you start the truck?

You need to pull the codes. Go to fordfuelinjection.com and look for how to run a self test if you do not know how to.

If you are getting an O2 sensor code that the truck is running rich, well i wouldn't suggest the O2 is bad. Because with 58psi at the rail... he!! yeah it is going to run rich and suck the fuel down. IDK how much pressure could mess up the diphagram in the FPR but id bet that it wouldnt last long.

Either the FPR is bad or something is up with your pumps. There is something fishy about your fuel delivery system. I do not know for sure the details of these systems just yet, but i know that 58psi is not good. Also, with a leak down on pressure, either you have one or more leaking injectors or there is a check valve or something or other that controls the fuel backflow that may be stuck open.

 

The 4.9L equipped trucks run at a higher pressure. 58 is normal under key on,engine off conditions. Same could be said for engine running, vacuum hose removed from the FPR or full throttle. I did ask previously what conditions that pressure was taken at. I would expect something lower with the engine running at idle with the vacuum hose attached.

 

oops! must have missed the 4.9L part of the post my apologies. I'll just shut up now

 

It's all good... I almost jumped on that myself.

 

ok changed map sensor and all vacum lines new intake gaskets and throttle body gaskets still same issue im thinking maybe the computer is fried i noticed none of my gauges are working correctly. today when driving truck started smooth out running about 45 in 4th gauges went to normal for about a minute then it when back to same crappy no power rich running stumbling condition

 

That sounds like a bad ground.

 

btw update found out o2 sensor code is irrelevant talked to previous owner he said o2 been dissconnected for years just test drove truck with a vacum port open and map sensor unhooked and it runs fine map sensor has been replaced twice this week my question is why does the truck run good with a vacum line leak im thinking maybe pcv valve is plugged? causing excessive vacum maybe my vacum gauge is wacked

 

Driving around with the O2 sensor disconnected forces the truck to run in open loop mode. Not necessarily a good thing. A bad PCM is a remote possibility. A quick check is to open up the lid and look for leaking capacitors and/or burn marks on the board.

As another reply indicated a bad ground could cause issues as well. IIRC the PCM ground is located on the passenger side fender well next to the starter relay/battery.

Looking back through this saga I need to ask, what were the codes by number?

 

If your gauges are jumping around then try this for a sec.
Disconnect the speed sensor on the rear dif and see if it stops sputtering.