Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairMedium
A technician is diagnosing a vehicle that experiences a noticeable loss of power under heavy acceleration and black smoke from the exhaust. During diagnosis, the technician measures the fuel pressure and finds it to be significantly higher than specifications. Which of the following is the MOST likely cause?
- AA clogged fuel injector
- BA weak fuel pump
- CA restricted fuel filter
- DA faulty fuel pressure regulator
Show answer & explanationAnswer & explanation
Correct answer: D. A faulty fuel pressure regulator
High fuel pressure indicates that the fuel pressure regulator is likely failing to properly reduce the pressure, leading to an overly rich mixture and black smoke.
Why the other options are wrong
- A. A clogged fuel injector would restrict fuel flow to a cylinder, potentially causing a lean condition or misfire, not high overall system pressure.
- B. A weak fuel pump would result in low fuel pressure and a lean condition, not high pressure.
- C. A restricted fuel filter would cause low fuel pressure, not high.
Fuel Pressure Regulator (FPR) Malfunction
A faulty fuel pressure regulator can lead to incorrect fuel pressure, causing either too lean or too rich an air-fuel mixture.
- High fuel pressure often indicates a regulator stuck closed or malfunctioning.
- Low fuel pressure can indicate a regulator stuck open or a weak pump.
- Incorrect fuel pressure affects engine performance and emissions.
Memory trick: Fuel's flow and pressure, regulator's measure, engine's pleasure.