ASE4 Ignition System Diagnosis and Repair

Question 1

A technician finds a spark plug with a black, sooty deposit. This condition indicates:

Accepted Answer

A rich fuel mixture or oil fouling

Answer

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:

Accepted Answer

Within specification and serviceable

Answer

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:

Accepted Answer

Too high — the wire should be replaced

Answer

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:

Accepted Answer

Weak ignition coil output under high demand

Answer

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?

Accepted Answer

To ionize the spark plug gap and initiate combustion

Answer

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.

ASE4 - ASE Automobile Engine Performance Practice Test