Hi i narrowed my lean condition to fuel system, now im getting code for fuel rail pressure sensor high resistance, some days OBD shows 76psi, some days normal 38psi, however no slight change in engine running. I replaced FRPS for new bosch(not listed for 5.4 but up to 4.6 as it was cheapest and quickest option) no change at all.
So i believe it must be electrical problem between FRPS/PCM/Fuel pump or FPDM....
Anyone has had similar problem and can send me to right direction?
Found this: 'The FPDM is energized at the same time the dome light is commanded on. A disabled or malfunctioning dome light does not affect the FPDM control.'
I know it should not affect but my dome light was full of watter and melted however when disconnected no change....just a thought!

 

I should say that i replaced FPDM for Dorman and was not able to remove ground bolt so i cut wrap and tested small circuit with frame, not sure if that proves anything.
FPDM cycle seems to be stuck at 16% all the time.
Must say engine run bit better(less shake, bank1 fuel trim only in +plus 10%ish( against +25%) when OBD shows 77psi(against 38psi) on idle.