The fuel pressure regulator/metering valve is not controlling rail pressure as expected.
SYMPTOMS
- Check-engine light
- Hard start
- Rough running
- Power loss
LIKELY CAUSES
- Faulty pressure regulator/metering valve
- Worn high-pressure pump
- Clogged filter
- Sensor fault
DIAGNOSIS STEPS
- Compare commanded vs actual rail pressure
- Test the regulator/metering valve
- Inspect the high-pressure pump
RELATED PARTS
- Fuel pressure regulator
- High-pressure fuel pump