Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairMedium
A vehicle with a port fuel injection system exhibits a long crank time, especially after sitting for several hours. Once started, the engine runs normally. The technician suspects a fuel system issue. Which of the following tests would be MOST appropriate to diagnose this specific symptom?
- AFuel pressure regulator vacuum line test.
- BFuel pump volume test.
- CFuel injector resistance test.
- DFuel pressure leak-down test.
Show answer & explanationAnswer & explanation
Correct answer: D. Fuel pressure leak-down test.
A long crank time after sitting for hours suggests a loss of residual fuel pressure. A fuel pressure leak-down test directly measures how well the fuel system maintains pressure after the engine is shut off, indicating if a component (like a check valve or injector) is allowing pressure to bleed off.
Why the other options are wrong
- A. A fuel pressure regulator vacuum line test would check for a vacuum leak affecting the regulator, which typically causes running issues, not just long crank after sitting.
- B. A fuel pump volume test measures the amount of fuel delivered per unit of time, which is important for overall performance but less specific to a long crank after sitting than a leak-down.
- C. A fuel injector resistance test checks for electrical faults in the injector, which would likely cause misfires or engine running problems, not specifically a long crank after sitting.
Fuel Pressure Leak-Down Test
A diagnostic test that measures how quickly the fuel system loses residual pressure after the fuel pump is turned off.
- Identifies leaks in the fuel pump check valve, fuel injectors, or fuel lines.
- Crucial for diagnosing long crank times or hard starts after sitting.
- Requires a fuel pressure gauge and monitoring pressure over time.
Memory trick: Long crank, no fuel tank, pressure's sank.