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Question

Difficulty: MediumIgnition System

During a routine tune-up on a gasoline engine, a technician notices that the spark plug electrode gaps have worn significantly wider than the factory specification. How does an excessively wide spark plug gap affect the ignition system's operation?

  1. The ignition coil must generate a higher secondary voltage to jump the gap, increasing the risk of misfire under load.Answer
  2. B
    The alternator is forced to output high-voltage AC current directly to the spark plugs to bridge the wider gap.
  3. C
    The spark plug discharges prematurely during the intake stroke rather than near top dead center of the compression stroke.
  4. D
    The wider gap creates a lean fuel condition by drawing unmetered air directly into the combustion chamber.

Answer

The ignition coil must generate a higher secondary voltage to jump the gap, increasing the risk of misfire under load.
An excessively wide spark plug gap increases the electrical resistance across the open space between the center and ground electrodes. To bridge this increased gap, the ignition coil must produce a significantly higher secondary voltage. Under heavy engine acceleration or load—when cylinder pressure is highest—the required firing voltage may exceed the maximum voltage available from the coil, resulting in an ignition misfire.

Step-by-Step Solution

1
Analyze how spark plug electrode gap affects electrical resistance across the plug tip.
A larger gap between the center electrode and ground electrode creates greater dielectric resistance.
Air and compressed fuel-air vapor act as electrical insulators that require sufficient potential difference to ionize.
2
Determine the impact of increased gap resistance on the ignition coil's secondary circuit.
The secondary winding must build to a higher kilovolt level before current can arc across the wider gap.
Secondary voltage rises until it reaches the breakdown voltage required to jump the spark plug gap.
3
Assess the operational consequence on engine performance when required voltage approaches available coil output.
If required voltage exceeds available coil capacity under high engine load, the plug fails to fire, causing an ignition misfire.
High cylinder pressures under load further increase resistance, causing weak or missing sparks when gaps are oversized.

Key Concept

Spark plug gap resistance and secondary ignition voltage demand
Estimated Time:1m 0s
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Topics

Ignition System

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