Hey Guys ---

No sarchasm intended here but you have gone off track on this one from the very beginning.

First off - FUEL PRESSURE IS MEANINGLESS without considering manifold vacuum. According to the above post your FDPM / fuel pump / filter and everything is acting generally as it should but you're looking in the wrong place.

Fuel injector delivery is rated at 'X' pounds of fuel per hour at a given pressure across the injector - from input to output nozzel. Any change in pressure differential across the injector would change the amount of fuel it delivers in each given millisec pulse width. THUS, the fuel system is designed to keep a 'constant pressure' accross the injector from input to nozzel, (without return line). The NOZZEL is sitting in a vacuum (relative to atmospheric pressure), and EVERYTHING ELSE is sitting in atmospheric pressure. Therefore the FDPM must adjust fuel pump output based on intake maniild vacuum. The Fuel Rail Pressure sensor provides the PCM a pressure reading that is 'relative to manifold vacuum'. (The fuel rail pressure sensor is connected to a vacuum port on the bottom passenger side of the intake manifold).

The fuel rail pressures @Bartak1 posted are correct - but they are 'relative to intake vacuum' --- NOT what you would see on a gauge at the fuel pump output or fuel rail input.

Thus your 20psi reading at idle (maximum vacuum, say around ~ 23 In Hg) would be (23 X 0.491154) plus the 20 pounds reading (atmospheric only) is actually around 31.296542. This _MIGHT_ be a little low, but I say around because idle vacuum is unknown. But you say it increases to around 30 with acceleration - and that confirms the PCM is commanding an increase in duty cycle to the FDPM - increasing the pressure because intake manifold vacuum declined.

I'm not suggesting I know what's wrong. May simply be a bad or leaky vacuum reference line to the FRP sensor. But I simply point out that fuel rail perssure readings should be taken by a live data scanner through OBDII (the PCM) so you know what "THE PCM" thinks fuel rail pressure is and what it is commanding the FDPM to do. That is all effected by the intake manifold vacuum at any given moment.

If you use the Torque Pro App, I worked out and posted a gauge that gives Fuel Pump Pressure (as would be read by a gauge 't'ed into the fuel rail pressure) here: https://www.f150forum.com/f4/5-4-3v-...8/#post5302229

 

Hi guys, my f-250 '06 5.4l triton crank but no start. Nothing in the sproeder valve on fuel rail(fuel pressure) no spray,no drop and no smell. Tank full. No code. All fuses and relays ok. Running good last time driven. Waht is that?

 

Fuel pump or FPDM died, inertia switch tripped, wiring issue, plugged fuel filter.