Spark Plugs: Inspection

Spark Plug Usage

• Ensure that the correct spark plug is installed. An incorrect spark plug causes driveability conditions. See SPARK PLUGS under IGNITION SYSTEMS in SERVICE & ADJUSTMENT SPECIFICATIONS - 2.2L CAVALIER & SUNFIRE article for the correct spark plug.
• Ensure that the spark plug has the correct heat range. An incorrect heat range causes spark plug fouling (colder plug), pre-ignition, causing spark plug and/or engine damage (hotter plug).

Inspection

1. Check the terminal post for damage. Check for a bent or broken terminal post. See Fig 1. Check for a loose terminal post by twisting and pulling the post. The terminal post should NOT move.
2. Check 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. Check for the spark plug boot for damage. Check 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.
3. Check the insulator for cracks. All or part of the electrical charge may arc through the crack instead of the electrodes.
4. Check for evidence of improper arcing. Measure the gap between the center electrode and the side electrode terminals. Spark plug gap should be 0.045" (1.14 mm). An excessively wide electrode gap can prevent correct spark plug operation. Check for the correct spark plug torque. See TORQUE SPECIFICATIONS . Insufficient torque can prevent correct spark plug operation. An over torqued spark plug, causes the insulator to crack. Check for signs of tracking that occurred near the insulator tip instead of the center electrode. Check for a broken or worn side electrode. Check 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. Check for bridged electrodes. Deposits on the electrodes reduce or eliminates the gap. Check for worn or missing platinum pads on the electrodes. If equipped. Check for excessive fouling.
5. Check 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.

Fig 1: Identifying Spark Plug Components

Courtesy of GENERAL MOTORS CORP.

Visual Inspection

• 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 rich fuel mixtures, leaking fuel injectors, excessive fuel pressure, restricted air filter element or incorrect combustion. Reduced ignition system voltage output, weak coils, worn ignition wires or incorrect spark plug gap. 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 intensity. Most powdery deposits will not effect spark intensity unless they form into a glazing over the electrode.