ASE A1 Engine RepairGeneral Engine DiagnosisHard
A technician is diagnosing an engine that occasionally requires extended cranking time before starting, especially after the vehicle has been sitting for several hours. Once started, the engine runs smoothly. Which of the following is the MOST likely cause?
- AA leaking fuel pressure regulator
- BA faulty crankshaft position sensor
- CA clogged fuel filter
- DWorn spark plugs
Show answer & explanationAnswer & explanation
Correct answer: A. A leaking fuel pressure regulator
Extended cranking after sitting indicates a loss of residual fuel pressure. A leaking fuel pressure regulator (or a leaking injector) allows fuel to drain back into the tank or manifold, requiring the fuel pump to re-pressurize the system before starting.
Why the other options are wrong
- B. A faulty crankshaft position sensor would typically cause no start, intermittent stalling, or misfires, not just extended cranking after sitting.
- C. A clogged fuel filter would restrict fuel flow under load, causing hesitation or stalling, not typically just extended cranking at startup.
- D. Worn spark plugs would cause misfires, rough idle, and general poor performance, not specifically extended cranking after a soak.
Hard Start (Extended Crank) Diagnosis
Extended cranking time before an engine starts often points to issues with fuel pressure retention or ignition immediately after a soak.
- Loss of residual fuel pressure is a primary cause.
- Common culprits: Leaking fuel pressure regulator or leaking fuel injector.
- Also potential: Weak fuel pump, faulty check valve.
Memory trick: Long crank after rest, fuel pressure's the test.