Hi name is bret. I'm new here and really need help. I have a 2007 cx7 that has a p0091 code. It's hard to start most of the time and when I'm driving it seems find but as I try to step on it or going up a hill it has no power. I just put in a used but good hpfp and didn't seem to help. I'm at a lose what it could be

 

Your code is definitely pointing a finger at the high pressure fuel pump or it's circuit. If the low pressure pump is not doing it's job, it will affect the HPFP. I would have to start with fuel pressure readings for both pumps first.

 

DTC P0091

Fuel pressure regulator control circuit low

DETECTION CONDITION
• When the PCM turns the spill valve control solenoid valve off but the spill valve control solenoid valve control circuit voltage is low, the PCM determines that the spill valve control solenoid valve control circuit has malfunction.
MONITORING CONDITIONS
― The following conditions are met:
• Engine speed is 3,000 rpm or less.
• Battery voltage is 10 V or more.
Diagnostic support note
• This is a continuous monitor (CCM).
• The MIL illuminates if the PCM detects the above malfunction condition during the first drive cycle.
• FREEZE FRAME DATA is available.
• DTCs are stored in the PCM memory.
POSSIBLE CAUSE
• Spill valve control solenoid valve malfunction connector or terminal malfunction
• Short to ground in the wiring harness between high pressure fuel pump terminal A and PCM terminal 2F
• Short to ground in the wiring harness between high pressure fuel pump terminal B and PCM terminal 2G
• Spill valve control solenoid valve malfunction
• PCM connector or terminal malfunction
• Open circuit in the wiring harness between high pressure fuel pump terminal A and PCM terminal 2F
• Open circuit in the wiring harness between high pressure fuel pump terminal B and PCM terminal 2G
• PCM malfunction