Inspection & Gapping
- 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, 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 area of the cylinder head for moisture, such as oil, coolant, or water. A spark plug boot that is saturated causes 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 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 excess 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
- 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.
Removal & Installation
- Turn the ignition OFF .
- If you are replacing the engine right bank (rear) spark plugs, rotate the engine for service access
- Remove the spark plug wires from the spark plugs.
- Remove the spark plugs from the engine.
- Install the spark plugs.
- If the spark plugs are installed into a new cylinder head, tighten the spark plugs to 15 lb-ft (20 Nm). If the spark plugs are installed into an existing cylinder head, tighten the spark plugs to 11 lb-ft (15 Nm).
- Install the spark plug wires to the spark plugs.