Spark Plug: Inspection
WARNING: This page is about a different car, the 2003 GMC Safari and 2003 Chevrolet Astro. However, it is still accessible from the selected car via links, so may be relevant.
- Ensure that the correct spark plug is installed. Ensure that the spark plug has the correct heat range. Colder range spark plug causes fouling. Hotter range causes pre-ignition, causing spark plug and/or engine damage. Inspect for a bent or broken terminal post. See Fig 1 . 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 soot. This is caused by the electrical charge traveling across the insulator between the terminal post and 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 terminals. 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 loose 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.
- A spark plug with Brown to Grayish-Tan color with small amounts of White powdery deposits are normal combustion by-products from fuels with additives. Carbon Fouled plugs with dry, fluffy Black carbon, or soot are caused by rich fuel mixtures or reduced ignition system voltage output. 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, such as oil, coolant, or additives that include substances such as silicone, (which produces very White coating), reduces the spark intensity. Most powdery deposits will not effect spark intensity unless they form into a glazing over the electrode.