- Verify that the correct spark plug is installed. An incorrect spark plug causes driveability conditions.
Ensure that the spark plug has the correct heat range. An incorrect heat range causes the following conditions:
- Inspect the terminal post for damage.
- Inspect for a bent or broken terminal post
- Test for a loose terminal post by twisting and pulling the post. The terminal post should not move.
- Inspect the insulator for flashover or carbon tracking, or soot. This is caused by the electrical charge traveling across the insulator between the terminal post and ground. Inspect for the following conditions:
- Inspect the spark plug boot for damage.
- Inspect the spark plug recess are of the cylinder head for moisture, such as oil, coolant, or water. A spark plug boot that is saturated will cause arcing to ground.
- Inspect the insulator for cracks. All or part of the electrical charge may arc through the crack instead of the electrodes.
- Inspect for evidence of improper arcing.
- Measure the gap between the center electrode and the side electrode. An excessively wide electrode gap can prevent correct spark plug operation.
- Inspect for the correct spark plug torque. Insufficient torque can prevent correct spark plug operation. An over torqued spark plug, causes the insulator to crack.
- Inspect for signs of tracking that occurred near the insulator tip instead of the center electrode.
- Inspect for a broken or worn side electrode.
Inspect for a broken, worn, or loose center electrode by shaking the spark plug.
- A rattling sound indicates internal damage.
- A looses center electrode reduces the spark intensity.
- Inspect for bridged electrodes. Deposits on the electrodes reduce or eliminates the gap.
- Inspect for worn or missing platinum pads on the electrodes, if equipped.
- Inspect for excessive fouling.
- 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.
Normal operation-Brown to grayish-tan with small amounts of white powdery deposits are normal combustion by-products from fuels with additives.
Carbon fouled-Dry, fluffy black carbon, or soot caused by the following conditions:
Rich fuel mixtures: Possible causes:
Leaking fuel injectors
Reduced ignition system voltage output: Possible causes:
Weak ignition coils
- 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 plug intensity. Most powdery deposits will not affect spark plug intensity unless they form into a glazing over the electrode.
Removal & Installation
3.5L & 3.7L Engines
Hummer H3 2006-2010
- Remove the ignition coils.
Clean the spark plug recesses with low pressure air.
CAUTIONAllow the engine to cool before removing the spark plugs. Attempting to remove the spark plugs from a hot engine may cause the plug threads to seize, causing damage to cylinder head threads.
- Remove the spark plugs from the cylinder head.
- Inspect the spark plugs.
Measure the spark plug gap on the spark plugs to be installed. Compare the measurement to the gap specifications.
NOTEBe sure that the spark plug threads smoothly into the cylinder head and the spark plug is fully seated. Use a thread chaser, if necessary, to clean threads in the cylinder head. Cross-threading or failing to fully seat the spark plug can cause overheating of the plug, exhaust blow-by, or thread damage.
- Install the spark plugs to the cylinder head. Tighten the plugs to 13 ft. lbs. (18 Nm).
- Install the ignition coils.
Hummer H3 2006-2010
- Remove the spark plug wire.
- Loosen the spark plug 1-2 turns.
- Brush or using compressed air, blow away any dirt from around the spark plug.
Remove the spark plug.
NOTEIf removing more than one plug, place each plug in a tray marked with the corresponding cylinder number.
- Inspect the spark plug gap. Adjust the gap as needed.
- Hand start the spark plug in the corresponding cylinder.
- Tighten the spark plug. Tighten the plug to 15 ft. lbs. (20 Nm).
- Install the spark plug wire.