Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairMedium
A technician is diagnosing an engine that intermittently stalls after heavy acceleration, particularly when coming to a stop. No DTCs are stored. During a test drive, the technician observes that the fuel pressure drops significantly during deceleration. What is the MOST likely cause?
- AA leaking fuel injector.
- BA restricted exhaust system.
- CA clogged fuel filter.
- DA faulty fuel pump check valve.
Show answer & explanationAnswer & explanation
Correct answer: D. A faulty fuel pump check valve.
A faulty fuel pump check valve would allow fuel pressure to drop excessively during deceleration (engine braking or closed throttle), as it's designed to maintain residual pressure and prevent fuel from flowing back to the tank. This sudden drop can starve the engine of fuel, causing it to stall.
Why the other options are wrong
- A. A leaking fuel injector would cause a rich condition, misfires, or hard starting, not typically a sudden fuel pressure drop during deceleration leading to a stall.
- B. A restricted exhaust system would cause a loss of power under acceleration and potentially overheating, but not directly a fuel pressure drop during deceleration.
- C. A clogged fuel filter would typically cause low fuel pressure under load (acceleration) and potentially a lean condition, not specifically a drop during deceleration leading to stall.
Fuel Pump Check Valve
The fuel pump check valve maintains residual fuel pressure in the system after the pump turns off and prevents fuel from flowing back to the tank, crucial for consistent pressure.
- Located within the fuel pump assembly.
- Prevents fuel drain-back.
- Failure causes extended cranking and pressure drop on deceleration.
Memory trick: Fuel pressure should hold steady; if it drops, the check valve is on vacation.