Hummer H2. Manual — part 1473

Fig. 168: Inspecting Spark Plug For Improper Arcing
Courtesy of GENERAL MOTORS CORP.

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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 . An excessively wide electrode gap can prevent correct spark plug
operation.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2

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Inspect for the correct spark plug torque. Refer to Ignition System Specifications . 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.

Spark Plug Visual Inspection

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Normal operation-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.

SPARK PLUG REPLACEMENT

Removal Procedure

1. Remove the spark plug wires. Refer to Spark Plug Wire Replacement .

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2

Fig. 169: View Of Spark Plug
Courtesy of GENERAL MOTORS CORP.

2. Loosen each spark plug 1 or 2 turns.

3. Brush or air blast away any dirt from around the spark plugs.

4. Remove the spark plugs 1 at a time. Place each plug in a tray marked with the corresponding cylinder

numbers.

Installation Procedure

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2

Fig. 170: View Of Spark Plug
Courtesy of GENERAL MOTORS CORP.

1. Properly position each spark plug washer.

2. Inspect each spark plug gap. Adjust each plug as needed.

Specification: Spark plug gap: 1.524 mm (0.060 in)

3. Hand start the spark plugs in the corresponding cylinders.

4. Tighten the spark plugs.

Tighten:

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For used heads tighten the spark plugs to 15 N.m (11 lb ft).

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For new aluminum heads tighten the spark plugs to 20 N.m (15 lb ft).

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For new iron heads, tighten the spark plugs to 30 N.m (22 lb ft).

5. Install the spark plug wires. Refer to Spark Plug Wire Replacement .

CRANKSHAFT POSITION (CKP) SENSOR REPLACEMENT

Removal Procedure

NOTE:

Refer to Fastener Notice in Cautions and Notices.

2004 Hummer H2

2004 ENGINE PERFORMANCE Engine Controls (Introduction) - 4.8L, 5.3L, and 6.0L - Hummer H2