I have looked in all my manuals and cannot find the fuel pressure specs for my '98 V6 Sohc. Dealer told me anywhere from 20-60psi was within spec, kind of a broad number. Another guy told me his '99 X was 60psi at the valve and another dealer told me 30psi with out the Vacum line and 40psi with it.
I measured my pressure at the fuel rail valve @ 28psi and it went down slightly when I revved the throttle. I have 137k mi on the engine. The problem is I am running a free flow intake and exhaust and the engine does not seem to be making the power in the upper range above 3000rpm.
I am convinced it is being fuel starved. I recently had the a/f ratio's proffesionaly calibrated to go along with the mods but no real change in performance. My guess is I either need a new fuel pump or Fuel Pressure Regulator. All induction components and Ignition components are good.