- 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
Observe the following service precautions:
Allow the engine to cool before removing the spark plugs. Attempting to remove spark plugs from a hot engine can cause the spark plugs to seize. This can damage the cylinder head threads.Clean the spark plug recess area before removing the spark plug. Failure to do so can result in engine damage due to dirt or foreign material entering the cylinder head, or in contamination of the cylinder head threads. Contaminated threads may prevent proper seating of the new spark plug.Use only the spark plugs specified for use in the vehicle. Do not install spark plugs that are either hotter or colder than those specified for the vehicle. Installing spark plugs of another type can severely damage the engine.
- 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.
It is important to check the gap of all new and reconditioned spark plugs before installation. Pre-set gaps may have changed during handling. Use a round wire feeler gauge to be sure of an accurate check, particularly on used plugs. Installing plugs with the wrong gap can cause poor engine performance and may even damage the engine. Gap the spark plugs to the specifications.
Be sure plug threads smoothly into cylinder head and is fully seated. Use a thread chaser if necessary to clean threads in cylinder head. Cross-threading or failing to fully seat spark plug can cause overheating of plug, exhaust blow-by, or thread damage. Follow the recommended torque specifications carefully. Over or under-tightening can also cause severe damage to engine or spark plug.
Use the correct fastener in the correct location. Replacement fasteners must be the correct part number for that application. Fasteners requiring replacement or fasteners requiring the use of thread locking compound or sealant are identified in the service procedure. Do not use paints, lubricants, or corrosion inhibitors on fasteners or fastener joint surfaces unless specified. These coatings affect fastener torque and joint clamping force and may damage the fastener. Use the correct tightening sequence and specifications when installing fasteners in order to avoid damage to parts and systems.
- 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.