I have a '95 F150 5.8 with a rebuilt engine. After the rebuild, the truck sat for 2 years because the fuel pumps stopped working and other unrelated problems. I finally replaced both pumps and the relay switch, and I get a steady 30 pounds of pressure with the engine running and FPR vacuum line connected, 40 pounds when vacuum line is disconnected. With help from F150 threads, I successfully diagnosed and resolved the EGR System, ultimately replacing all vacuum lines, the EGR valve, Solenoid and EVP sensor. No more Engine codes; the truck runs pretty well and passed emissions. Now to my current problem; When the engine is cold it starts very rough, for 10 to 15 seconds, then smooths out and runs very well; However, once it gets to operating temperature a rough idle develops. In park it runs smooth with an occasional miss. In drive it runs smooth for a several minutes, begins to idle rough, then smooths out for a few minutes, then rough idle again. I suspect the FPR, but other than removing the vacuum line, I'm not sure how to diagnose it. Even though the fuel pumps are new Precision pumps from O'Reilly, could it be they don't produce enough pressure?

 

Are you getting any Check Engine lights or have you pulled the codes to see whether the computer has flagged anything?

By idling rough, I'm assuming you mean spitting and sputtering rather than surging which would point to the IAC as a leading suspect?

Perhaps pull the vacuum line off the FPR to look for any fuel on the vacuum side which may indicate a diaphragm issue. Fuel pressure seems a bit low, would like to see 35-40, but don't see that as causing your current issues unless the pressure isn't remaining stable. No tests that I am aware of for the FPR.

Perhaps one or more injectors are not sealing off, or leaking down, or not misting properly causing the starting issues and issues at idle? Professional injector cleaning services are available to run their stuff through, but have had good results here running a couple cans of SeaFoam or Berryman's B12 through. Maybe a red herring, but with it sitting, wonder whether the injectors have gummed up a bit? Suggest not to go replacing injectors, failure rates seem to be rather low bordering on non-existent.

Kinda reaching here with the above, hopefully other members will be along shortly to chime in with their ideas.

 

I’ve gotten no codes since I fixed the EGR system. Yes I do mean sputtering. I considered injectors and ran Lucas through the system. I’ll try Berryman’s to see if it helps. I had a loose injector connection and replaced the connector. It seems to be fine now. Another symptom is the rough idle seems worse when I switch to the rear tank.