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Question

Difficulty: EasyIgnition System

During a routine engine tune-up, a technician uses a feeler gauge to measure and adjust the clearance between the center electrode and the ground electrode of each spark plug. What is the primary purpose of setting this specific spark plug gap?

  1. To ensure an electrical arc of sufficient energy forms to properly ignite the compressed air-fuel mixtureAnswer
  2. B
    To regulate the charging rate supplied to the battery by the alternator during engine operation
  3. C
    To control the volume of intake air entering the cylinder to prevent a lean mixture condition
  4. D
    To prevent exhaust gases from escaping prematurely during the four-stroke compression cycle

Answer

Setting the proper spark plug gap ensures an electrical arc of sufficient energy forms to properly ignite the compressed air-fuel mixture.
Maintaining the specified spark plug gap ensures that the secondary ignition voltage creates an electrical arc with sufficient energy to ignite the air-fuel mixture cleanly without causing ignition coil overload or spark blowout under cylinder compression.

Step-by-Step Solution

1
Identify the primary function of the spark plug in the ignition system.
The spark plug provides the physical air gap across which high secondary voltage arcs to initiate combustion.
The ignition system must reliably ignite the air-fuel mixture near the end of the compression stroke.
2
Analyze how electrode spacing influences spark formation and combustion.
A correctly gapped plug balances the voltage required to jump the gap with the arc duration needed for clean combustion.
A gap that is too wide can cause ignition misfires under cylinder compression, while a gap that is too narrow creates a weak spark that causes incomplete combustion.

Key Concept

Spark Plug Electrode Gap and Ignition Discharge
Estimated Time:45s
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Topics

Ignition System

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