Inspection & Gapping
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 (short trips).
Wet Fouling or 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 and reinstalling the fouled 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 can be cleaned using standard procedures.
Scavenger Deposits: 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 standard procedures.
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: Pre-ignition damage is usually caused by excessive combustion chamber temperature. The center electrode dissolves first and the ground electrode dissolves somewhat latter. 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 electrodes 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 0.001 inch per 2000 miles 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
Grasping the spark plug boot firmly and with a twisting pulling motion, disconnect the spark plug wires from the spark plugs.
NOTEIf an original spark plug is reused, install it in the same cylinder from which it was removed. New spark plugs can be used in any cylinder.
NOTEUse compressed air to remove any debris from the spark plug well before removing the spark plugs.
- Remove the spark plugs.
- Inspect the spark plugs. If necessary, clean the spark plugs with a wire brush or a professional spark plug cleaner (follow the manufacturer's instructions).
- Adjust the spark plug gap as required.
- Set gap to 0.052-0.056 inches (1.3-1.4mm).
Install the spark plugs.
NOTEWhenever an ignition wire is reinstalled, or a new one is installed, apply dielectric compound to the interior surface of the spark plug wire boot.
- Connect the ignition wires to the spark plugs.