Spark Plug Inspection
Courtesy of GENERAL MOTORS CORP.
- Inspect the terminal post (1) for damage.
- 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 for carbon tracking soot. This condition is caused by the electrical charge travelling 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 from such as oil, coolant, or from water. A saturated spark plug boot causes arcing to ground.
- Inspect the insulator (2) for cracks. All or part of the electrical charge may arc through the crack instead of through the electrodes (3, 4).
- Inspect for evidence of incorrect arcing.
- Measure the gap between the centre electrode (4) and the side electrode (3) terminals. Refer to Ignition System Specifications
.
- 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.
- Inspect for signs of tracking that occurred near the insulator tip instead of at the centre electrode (4).
- Inspect for a side electrode (3) that is broken or worn.
- Inspect for a broken, worn, or loose centre electrode (4) by shaking the spark plug.
- A rattling sound indicates internal damage.
- A loose centre electrode (4) reduces the spark intensity.
- Inspect for bridged electrodes (3 and 4). Deposits on the electrodes reduce or eliminate the gap.
- Inspect for worn or missing platinum pads on the electrodes (3 and 4), 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.