ASE A1 Engine RepairFuel, Emissions, and Ignition Systems (General)Medium
A vehicle exhibits a prolonged crank time but eventually starts. The technician connects a fuel pressure gauge and observes that the fuel pressure drops rapidly after the engine is shut off. What is the most likely cause of this condition?
- AA leaking fuel injector or faulty fuel pump check valve
- BA faulty fuel pressure regulator that is stuck open
- CA restricted fuel filter
- DAn over-pressurized fuel system
Show answer & explanationAnswer & explanation
Correct answer: A. A leaking fuel injector or faulty fuel pump check valve
A rapid drop in fuel pressure after the engine is shut off indicates a leak in the fuel system, allowing pressure to bleed off. The most common culprits for this symptom are a leaking fuel injector or a faulty check valve within the fuel pump assembly.
Why the other options are wrong
- B. A faulty fuel pressure regulator stuck open would lead to consistently low fuel pressure during engine operation, rather than a rapid drop after shut-off while the pump is inactive.
- C. A restricted fuel filter would typically cause low fuel pressure during engine operation, not a rapid drop after shut-off.
- D. An over-pressurized fuel system would likely cause rich running conditions or engine flooding, not a rapid pressure drop after shut-off.
Fuel Pressure Leak Down
The rapid decrease of fuel pressure in the system after the engine is turned off, indicating a leak or faulty component allowing pressure to escape.
- Often causes extended crank times.
- Can be due to leaking injectors or a faulty fuel pump check valve.
- Diagnosed by monitoring fuel pressure after engine shutdown.
Memory trick: Pressure drops, engine stalls, check for leaks, or it's a false start.