Special care should be taken when installing spark plugs into the cylinder head spark plug wells. Be sure the plugs do not drop into the plug wells as electrodes can be damaged.
Always tighten spark plugs to the specified torque. Over tightening can cause distortion resulting in a change in the spark plug gap or a cracked porcelain insulator. Proper torque is especially important in the case of aluminum cylinder heads.
When replacing the spark plug and ignition coil cables, route the cables correctly and secure them in the appropriate retainers. Failure to route the cables properly can cause the radio to reproduce ignition noise. It could cause cross ignition of the spark plugs or short circuit the cables to ground.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.
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).
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.
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. Spark plugs that have normal wear can usually be cleaned, have the electrodes filed, have the gap set and then be installed.
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. This rust color can be misdiagnosed as being caused by coolant in the combustion chamber. Spark plug performance may be affected by MMT deposits.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.
Preignition 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 electrodes porcelain insulator).
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.
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.
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.
Removal & Installation
Each individual spark plug is located under each ignition coil. Each individual ignition coil must be removed to gain access to each spark plug. Refer to Ignition Coil Removal/Installation. Prior to removing a spark plug, spray compressed air around base of the ignition coil at cylinder head. This will help prevent foreign material from entering combustion chamber.
- Remove spark plug from cylinder head using a quality socket with a rubber or foam insert.
- Inspect spark plug condition.
- Start the spark plug into the cylinder head by hand to avoid cross threading.
- Before installing coil(s), check condition of coil O-ring and replace as necessary. To aid in coil installation, apply silicone to coil O-ring.
- Tighten spark plugs to 20 ft. lbs. (27 Nm) torque.
- Install ignition coil(s). Refer to Ignition Coil Removal/Installation.