The engine uses platinum tip resistor spark plugs. Platinum-tip spark plugs allow 100,000-mile (161,000-km) replacement intervals in normal service. They have resistance values of 6,000 to 20,000 ohms when checked with at least a 1 kV tester. Do not use an ohm meter to check the resistance of the spark plugs as this will give an inaccurate reading. Spark plugs using either a single or double platinum tips have a recommended service life of 100,000 miles for normal driving conditions. The spark plugs have a recommended service life of 75,000 miles for severe driving conditions. A thin platinum pad is welded to both or just the center electrode (2) end(s). Extreme care must be used to prevent spark plug cross threading, incorrect gapping, and ceramic insulator damage during plug removal and installation.
Inspection & Gapping
The few deposits present on the spark plug will probably be light tan or slightly gray in color. This is evident with most grades of commercial gasoline. There will not be evidence of electrode burning. Gap growth will not average more than approximately 0.001-inch (0.025 mm) per 2,000 miles (3200 km) of operation. Some fuel refiners in several areas of the United States have introduced a manganese additive (MMT) for unleaded fuel. During combustion, fuel with MMT causes the entire tip of the spark plug to be coated with a rust-colored deposit, commonly misdiagnosed as coolant in the combustion chamber.
Cold Fouling/Carbon Fouling: Cold fouling is sometimes referred to as carbon fouling. The deposits that cause cold fouling are basically carbon. A dry, black deposit on one or two plugs in a set may be caused by sticking valves or defective spark plug cables. Cold/carbon fouling of the entire set of spark plugs may be caused by a clogged air cleaner element or repeated short operating times where the engine does not reach operating temperature.
Wet Fouling/Gas Fouling: A spark plug coated with excessive wet fuel or oil is wet fouled. In older engines, worn piston rings, leaking valve guide seals or excessive cylinder wear can cause wet fouling. In new or recently overhauled engines, wet fouling may occur before break-in (normal oil control) is achieved. This condition can usually be resolved by cleaning with solvent and reinstalling the plugs.
Oil or Ash Encrusted:
If one or more spark plugs are oil or oil ash encrusted, evaluate engine condition for the cause of oil entry
into that particular combustion chamber.
Electrode Gap Bridging:
Electrode gap bridging may be traced to loose deposits in the combustion chamber. These deposits accumulate on the spark plugs during continuous stop-and-go driving. When the engine is suddenly subjected to a high torque load, deposits partially liquefy and bridge the gap between electrodes. This short circuits the electrodes. Spark plugs with electrode gap bridging should be replaced.
Fuel scavenger deposits may be either white or yellow. They may appear to be harmful, but this is a normal condition caused by chemical additives in certain fuels. These additives are designed to change the chemical nature of deposits and decrease spark plug misfire tendencies. Notice that accumulation on the ground electrode and shell area may be heavy, but the deposits are easily removed. Spark plugs with scavenger deposits can be considered normal in condition and can be cleaned using solvent.
Chipped Electrode Insulator:
A chipped electrode insulator usually results from bending the center electrode while adjusting the
spark plug electrode gap. Under certain conditions, severe detonation can also separate the insulator from
the center electrode. Spark plugs with this condition must be replaced.
Pre-ignition damage is usually caused by excessive combustion chamber temperature. The center electrode
dissolves first and the ground electrode dissolves somewhat later. Insulators appear relatively deposit free. Determine if the spark plug has the correct heat range rating for the engine. Determine if ignition timing is over-advanced or if other operating conditions are causing engine overheating. (The heat range rating refers to the operating temperature of a particular type spark plug. Spark plugs are designed to operate within specific temperature ranges. This depends upon the thickness and length of the center electrode-s porcelain insulator.)
Spark Plug Overheating:
Overheating is indicated by a white or gray center electrode insulator that also appears blistered. The increase in electrode gap will be considerably in excess of the normal .001-inch (0.025 mm) per 2,000 miles (3,200 km) of operation. This suggests that a plug with a cooler heat range rating should be used. Over-advanced ignition timing, detonation and cooling system malfunctions can also cause spark plug overheating.
Removal & Installation
- Before servicing the vehicle, refer to the Precautions section.
- Disconnect battery negative cable from battery and properly isolate to prevent accidental reconnection.
Twist and pull the metal clad spark plug cable boots to remove them from the spark plugs.
NOTEAvoid allowing debris to fall into the spark plug holes during replacement.
Clean the cylinder head spark plug recesses using low-pressure compressed air.
WARNINGDo not use power tools to replace spark plugs. Damage to the cylinder head can result.
- Use a rubber insulated spark plug socket and a hand ratchet to remove the spark plugs.
Remove the spark plugs from the engine.
- Gap the spark plugs with a spark plug gap gauge to 0.040-inch (1.02 mm) before installation.
Start the spark plugs into the cylinder head by hand to avoid cross threading and tighten to 21 ft. lbs. (28 Nm)
NOTEWhen installing the spark plug cables, route the cables correctly. Failure to route the cables properly can cause improper spark plug phase shift (inductive cross fire).
Install the spark plug cables to the appropriate spark plug location.
- Refer to the reference pad cast into the cylinder head cover to identify proper spark plug/ spark plug cable orientation.
- Insure a positive connection is made. A snap should be felt when a good connection is made between the spark plug cable and the spark plug.