Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairMedium
A vehicle with a port fuel injection system experiences a hard start condition, especially after sitting for several hours. Once started, it runs fine. A fuel pressure leak-down test is performed, and the pressure drops rapidly after the fuel pump shuts off. Which component is the MOST likely cause?
- AA leaking fuel pump check valve
- BA clogged fuel injector
- CA restricted fuel filter
- DA faulty fuel pressure regulator
Show answer & explanationAnswer & explanation
Correct answer: A. A leaking fuel pump check valve
A rapid drop in fuel pressure after the pump shuts off indicates a leak in the system that is not external. The fuel pump check valve is responsible for holding residual pressure in the system, and if it leaks, fuel drains back to the tank, causing extended cranking.
Why the other options are wrong
- B. A clogged fuel injector would cause a lean condition in a specific cylinder, not a rapid drop in overall system pressure after shut-off.
- C. A restricted fuel filter would cause low pressure during operation, not a rapid leak-down after shut-off.
- D. A faulty fuel pressure regulator could cause incorrect operating pressure (high or low), but a leak-down issue after shut-off points more directly to the check valve or a leaking injector.
Fuel Pump Check Valve Failure
The fuel pump check valve maintains residual fuel pressure in the system after the pump turns off, preventing hard starts due to fuel draining back.
- Symptoms: Hard starts (especially after sitting), long crank times.
- Diagnostic: Rapid fuel pressure drop during a leak-down test.
- Located within or near the fuel pump assembly.
Memory trick: Pressure drop, check valve's flop, hard start won't stop.