ASE4 Ignition System Diagnosis and Repair 1 — Questions and Answers
Question 1: A technician finds a spark plug with a black, sooty deposit. This condition indicates:
- A lean fuel mixture
- A rich fuel mixture or oil fouling (Correct answer)
- Over-advanced ignition timing
- Normal combustion deposits
Correct answer: A rich fuel mixture or oil fouling
Black sooty deposits on a spark plug indicate a rich fuel mixture or oil entering the combustion chamber.
Question 2: An ignition coil primary resistance measures 0.5 ohms. The specification is 0.4–0.8 ohms. This means the coil is:
- Open and must be replaced
- Shorted and must be replaced
- Within specification and serviceable (Correct answer)
- Weak and should be replaced as a precaution
Correct answer: Within specification and serviceable
A primary resistance reading of 0.5 ohms falls within the 0.4–0.8 ohm specification, indicating the coil is serviceable.
Question 3: A spark plug wire shows 10,000 ohms of resistance per foot. This is considered:
- Normal for a carbon-core suppression wire
- Too high — the wire should be replaced (Correct answer)
- Too low — excessive current will damage the coil
- Acceptable only for distributor-type systems
Correct answer: Too high — the wire should be replaced
Spark plug wire resistance should not exceed approximately 10,000–12,000 ohms total; 10,000 ohms per foot is excessively high.
Question 4: An engine misfires only under heavy load. Spark plugs and wires test good. The NEXT most likely cause is:
- A faulty crankshaft position sensor
- Weak ignition coil output under high demand (Correct answer)
- A leaking injector
- A faulty MAP sensor
Correct answer: Weak ignition coil output under high demand
An ignition coil that tests marginally at rest may fail to produce adequate spark energy under the high demand of heavy load.
Question 5: What is the purpose of the secondary ignition system's high voltage?
- To power the ECM
- To ionize the spark plug gap and initiate combustion (Correct answer)
- To charge the battery during engine braking
- To operate the fuel injectors
Correct answer: To ionize the spark plug gap and initiate combustion
The secondary ignition system produces high voltage (20,000–40,000V) to ionize the gap at the spark plug and fire the air/fuel mixture.
Question 6: When diagnosing a no-start condition, the technician confirms no spark at any cylinder. The FIRST component to check is:
- Individual ignition coils
- The crankshaft position sensor (Correct answer)
- The spark plugs
- The ignition switch
Correct answer: The crankshaft position sensor
No spark at all cylinders points to a common input signal failure; the crankshaft position sensor is the most critical common trigger.
ASE4 Ignition System Diagnosis and Repair 1
A technician finds a spark plug with a black, sooty deposit.
This condition indicates: