On the 987.2 9A1 DFI engine, rail pressure is above the expected level. Usually a stuck or malfunctioning volume-control/pressure-regulator valve on the high-pressure pump, or a faulty rail-pressure sensor reporting incorrectly. Excess pressure can force rich running and stress injectors.
SYMPTOMS
- Check-engine light
- Rough running / possible misfire
- Fuel smell
- Hard start
LIKELY CAUSES
- Stuck volume-control / pressure-regulator valve on the HPFP
- Faulty rail-pressure sensor
- HPFP internal fault
- Wiring fault to the regulator valve
DIAGNOSIS STEPS
- Compare commanded vs actual rail pressure
- Test the volume-control / regulator valve
- Inspect the rail-pressure sensor and wiring
- Inspect the high-pressure pump
RELATED PARTS
- Fuel pressure regulator / volume-control valve
- High-pressure fuel pump (9A1)
- Fuel-rail pressure sensor