20psi fuel pressure on boosted 02' GT

[fivemustangs]

I was coming home the other night and gave it WOT at the passing lanes, after I got to the end I noticed my fuel pressure gauge was reading 20PSI during crusing speeds! when I listened there was a ping under boost so I took it easy the rest of the way home. The next day I started it and it was reading 30psi, so I replaced the fuel filter and nothing changed. I plugged in my SCT livewire and the data reading said it was running around 40psi were it should have been, but the autometer electric fuel gauge was still reading 30psi. I unplugged the vaccum and it went to 40psi then unplugged the sensor and the pressure went to 60PSI. When everything was connected and I rev'd the engine it would go to about 45-50 and then slowly drop to 20PSI and then pop back to 30psi at idle. Anyone have any idea what the issue might be? modes listed below but I have a focus 255 pump and KB boost-a-pump. But al connections seem to be in check. Thanks!!!

 

[fivemustangs]

bump.

 

[wmburns]

30 PSI guage seems correct to me. The fact the PCM FP jumps to 40 PSI when the vacuum reference line is disconnected, means the FRPS is seeing the intake vacuum. Remember at idle, the gauge fuel pressure should be less than 40 PSI (subtract the intake vacuum).

Disconnecting the FRPS electrical connector proves little. Other than how the PCM handles a FRPS failure.

IMO, the fact that the fuel pump is capable of producing high pressure means the pump is OK.

What I would look at is a bad/ruptured Fuel rail pressure sensor. BUt to know for sure, monitor the Fuel pump duty cycle. If it's very high, this indicates the fuel pump is maxed out. If very low, that means there is capacity left.

I know that it reads a correct 40 PSI at the PCM. But consider that if the sensor is not giving good values, the only knowledge of fuel pressure is what the FRPS gives. So the PCM will adjust the fuel pump to achieve a 40 PSI reading from the sensor.

 

[Don 95Vert]

On a returnless system, looking at FP doesn't tell you much, the PCM uses pressures drop across the injectors to maintain the target rail absolute pressure. You can log pressure drop with an SCT handheld and LiveLink, usually is 39-40.

 

[fivemustangs]

Well I took the car for a ride today and the fuel pressure was between 28 and 40 during cruise but when i down shifted the pressure would still drop to 5 psi and then jump back to 30. At times the car would be perfect and fluctuate between 35-40 were it usually was. WOT seemed to be ok today and hold at 44psi.