Automotive Service Excellence (ASE) A8 Engine PerformanceIgnition System Diagnosis and RepairMedium
A technician is diagnosing a vehicle with an intermittent misfire on cylinder #2. The misfire is more pronounced during humid weather. After inspecting the spark plug and coil, which appear normal, the technician decides to perform a leakage test. Which of the following tools or methods would be most effective for detecting high voltage leakage in the ignition system under these conditions?
- AA spray bottle with water and a dark environment.
- BA timing light to observe the spark plug firing.
- CA digital multimeter to check resistance of the coil primary.
- DA high-tension spark tester with a grounded lead.
Show answer & explanationAnswer & explanation
Correct answer: A. A spray bottle with water and a dark environment.
High voltage leakage, especially in humid conditions, can cause the spark to jump to ground before reaching the spark plug. Spraying water in a dark environment allows technicians to visually identify arcing or 'tracking' from ignition components, which is a direct indicator of leakage.
Why the other options are wrong
- B. A timing light shows when the spark fires, but not if it's leaking or weak due to leakage.
- C. A multimeter checks primary resistance, not secondary high voltage leakage.
- D. A spark tester checks if the coil is producing voltage, but not where that voltage might be leaking from the wires or coil boots.
High Voltage Leakage Detection
High voltage leakage occurs when ignition voltage escapes to ground before reaching the spark plug, often exacerbated by humidity, and can be visually detected by observing arcing in a dark environment.
- Causes misfires, especially in humid conditions.
- Can be seen as visible arcing in the dark.
- Often related to cracked insulation or poor connections.
Memory trick: Water and dark reveal the spark's hidden arc.