Spark Plug Inspection
Spark Plug Inspection |
Spark Plug Usage |
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Ensure that the correct spark plug is installed. An incorrect spark plug causes driveability conditions. Refer to the Electronic Parts Catalog.
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Ensure that the spark plug has the correct heat range. An incorrect heat range causes the following conditions:
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Spark plug fouling-Colder plug
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Pre-ignition causing spark plug and/or engine damage-Hotter plug
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Spark Plug Inspection |
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Inspect the terminal post (1) for damage.
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Inspect for a bent or broken terminal post (1).
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Test for a loose terminal post (1) by twisting and pulling the post. The terminal post (1) should NOT move.
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Inspect the spark plug boot for damage.
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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.
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Inspect the insulator (2) for cracks. All or part of the electrical charge may arc through the crack instead of the electrodes (3, 4).
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Inspect for evidence of improper arcing.
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Measure the gap between the center electrode (4) and the side electrode (3) terminals. Refer to
Ignition System Specifications (LAU)
Ignition System Specifications (LF1)
. An excessively wide electrode gap can prevent correct spark plug operation.
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Inspect for the correct spark plug torque. Refer to
Ignition System Specifications (LAU)
Ignition System Specifications (LF1)
. Insufficient torque can prevent correct spark plug operation. An over torqued spark plug, causes the insulator (2) to crack.
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Inspect for signs of tracking that occurred near the insulator tip instead of the center electrode (4).
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Inspect for a broken or worn side electrode (3).
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Inspect for a broken, worn, or loose center electrode (4) by shaking the spark plug.
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A rattling sound indicates internal damage.
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A loose center electrode (4) reduces the spark intensity.
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Inspect for bridged electrodes (3, 4). Deposits on the electrodes (3, 4) reduce or eliminates the gap.
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Inspect for worn or missing platinum pads on the electrodes (3, 4), if equipped.
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Inspect for excessive fouling.
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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.
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Spark Plug Visual Inspection |
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Normal: Brown to grayish-tan with small amounts of white powdery deposits are normal combustion by-products from fuels with additives.
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Carbon fouled-Dry, fluffy, black carbon or soot caused by the following conditions:
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Rich fuel mixtures
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Leaking fuel injectors
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Excessive fuel pressure
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Restricted air filter element
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Incorrect combustion
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Reduced ignition system voltage output
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Weak coils
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Worn ignition wires
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Incorrect spark plug gap
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Excessive idling or slow speeds under light loads can keep spark plug temperatures so low that normal combustion deposits may not burn off.
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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.
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