1998 5.4 engine problem — STUMPED

[Spaznaut]

30 psi isn't where you need to be on your fuel pressure. Think isn't closer to 40-50psi. Either your pump is weak or your repair has a restriction in it. Also the pressure regulator may have issues but depending on if the pump has even been changed I'd look there first. I replaced the original in my '99 with 285k miles last year.

 

[homermandy]

Quick update. I got a nicer obd2 scan tool which showed a bad cop on cylinder 1. Put a new one on and the engine runs much smoother. Still noticing a few odd things. After sitting overnight the fuel pressure slowly rises to 30 after cranking and running. Like a minute. When I smash throttle it stays and doesn’t drop. Any reason for slow build up of pressure?

I installed a brands new fuel pump and also fuel filter. I also had a rubber boot leak at throttle body so replaced that too.

 

[homermandy]

I also recorded some data when I was revving and idling. Short term fuel trim bank 1 0. Stft bank 2 0. Stft b1s1 0. Stft b1s2 99.22%. Stft b2s1 0. Stft b2s2 99.22%.