Automotive Service Excellence (ASE) A8 Engine PerformanceFuel, Air Induction, and Exhaust Systems Diagnosis and RepairEasy
A technician is diagnosing a vehicle that experiences a noticeable loss of engine power only when the fuel tank is less than a quarter full. The engine runs perfectly fine when the tank is more than half full. Which of the following is the MOST likely cause?
- AA faulty fuel pressure regulator
- BA restricted exhaust system
- CA clogged fuel filter
- DA failing fuel pump with a weak pickup
Show answer & explanationAnswer & explanation
Correct answer: D. A failing fuel pump with a weak pickup
When the fuel level is low, the fuel pump has to work harder to draw fuel, and a weak pickup or a failing pump will struggle under these conditions, leading to fuel starvation and power loss. As the fuel level increases, the pump is submerged and operates more efficiently.
Why the other options are wrong
- A. A faulty fuel pressure regulator would likely affect fuel pressure at all tank levels.
- B. A restricted exhaust system would cause power loss regardless of the fuel tank level.
- C. A clogged fuel filter would likely restrict fuel flow at all tank levels, not just when the tank is low.
Fuel Pump Weakness
A fuel pump that struggles to deliver adequate fuel pressure or volume, particularly under specific conditions like low fuel levels or high demand.
- Symptoms often worsen with low fuel levels.
- Can manifest as power loss, hesitation, or stalling.
- Often related to internal pump wear or clogged pickup screens.
Memory trick: Low tank, low power, pump's sour.