when i start my truck i see 58psi after a few minutes
it drops to 44psi, is the pressure controlled mechanically
or by elect ? PCM ? or a FPR ?
this is a returnless system.

 

NNBS 07+? FPCM is controlling that. Mine had same numbers.

 

how is the FPCM controlled ? from the PCM ?
it is a fixed unit or can it be adjusted/reprogrammed ?

 

It talks with ECM via a CAN communication link. Believe that the tables for it can be set to run 58psi at all times versus just bumping to 58psi at WOT. Do not believe you can adjust it for anything higher.

A boost-a-pump can apparently be wired in after the FPCM to increase voltage to the fuel pump as the FPCM controls the pump via pwm and will keep reducing voltage to the pump once it sees fuel pressure rising beyond set levels. I just converted to a return system and did away with the FPCM.