Document ID: 1835383

Spark Plug Usage

Ensure that the correct spark plug is installed. An incorrect spark plug causes driveability conditions. Refer to the Electronic Parts Catalog.

Spark Plug Inspection

Inspect the terminal post (1) for damage.

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Inspect for a bent or broken terminal post (1).
Test for a loose terminal post (1) by twisting and pulling the post. The terminal post (1) should NOT move.

Inspect the insulator (2) for flashover or carbon tracking, soot. This condition is often mistakenly identified as a cracked insulator. This is caused by the electrical charge traveling across the insulator (2) between the terminal post (1) and ground. Inspect for the following conditions:

Inspect the spark plug boot for damage.
Inspect the spark plug recess area of the cylinder head for moisture, such as oil, coolant, or water. A spark plug boot that is saturated causes arcing to ground.

Inspect the insulator (2) for cracks. All or part of the electrical charge may arc through the crack instead of the electrodes (3, 4).
Inspect for evidence of improper arcing.

A rattling sound indicates internal damage.
A loose center electrode (4) reduces the spark intensity.

Inspect the spark plug recess area of the cylinder head for debris. Dirty or damaged threads can cause the spark plug not to seat correctly during installation.

Spark Plug Visual Inspection

Rich fuel mixtures

Leaking fuel injectors
Excessive fuel pressure
Restricted air filter element
Incorrect combustion

Reduced ignition system voltage output

Weak coils
Worn ignition wires
Incorrect spark plug gap

Excessive idling or slow speeds under light loads can keep spark plug temperatures so low that normal combustion deposits may not burn off.

Deposit Fouling—Oil, coolant, or additives that include substances such as silicone, very white coating, reduces the spark intensity. Most powdery deposits will not effect spark intensity unless they form into a glazing over the electrode.

Note: Carbon on spark plug tower means carbon will also be on inside of spark plug wire boot or coil boot and will cause both new spark plug and spark plug wire or coil boot to fail again.

Operation	Task	Skill	Hours
Remove & Install	Ignition System · Spark Plugs, R&I	B	2.8
Remove & Replace	Ignition System · Spark Plugs, R&R	B	2.8

Spark Plug

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