ASE G1 Auto Maintenance and Light RepairEngine SystemsHard
A technician is diagnosing a vehicle that cranks but does not start. The spark plugs are wet with fuel, and a strong odor of gasoline is present. When a spark tester is used, there is no spark from any of the spark plug wires. What is the most likely issue?
- AA failed crankshaft position sensor
- BA low engine compression
- CA clogged exhaust system
- DA faulty fuel pump relay
Show answer & explanationAnswer & explanation
Correct answer: A. A failed crankshaft position sensor
If the spark plugs are wet with fuel (indicating fuel delivery) but there is no spark, the problem lies within the ignition system. A failed crankshaft position sensor is a common cause for a no-spark condition, as it provides the crucial timing signal for the ignition system to fire.
Why the other options are wrong
- B. Low engine compression would prevent combustion and could cause a no-start, but would not directly cause a complete absence of spark.
- C. A clogged exhaust system would impede exhaust flow and cause a no-start or poor running condition, but not a complete lack of spark.
- D. A faulty fuel pump relay would prevent fuel delivery, leading to dry spark plugs, which contradicts the 'wet with fuel' symptom.
No Spark, Fuel Present
When an engine cranks, receives fuel (wet plugs), but has no spark, the issue is typically in the primary ignition circuit, often a failed crankshaft position sensor or an issue with the ignition control module/ECM.
- Wet plugs = fuel delivery is good.
- No spark = ignition system fault.
- Crank sensor is crucial for spark timing.
Memory trick: No spark, fuel's fine, crank sensor's out of time.