The spark plugs are resistor type and taper seated. No gasket is used. Use a 6 point socket with a rubber insert when removing the plugs. Use a wire type feeler gage when measuring the plug gap. Bend the side ground electrode when adjusting the gap.

The spark plugs have platinum pads welded into the electrodes. These pads extend the life of the plugs to 160,000 kilometers (100,0000 miles). The ribless insulator and boot design identifies the spark plug and provides better plug to boot retention. This design also reduces carbon tracking and engine misfire.

Normal plug operation consists of idling, highway driving, and "stop and go" driving. Normal spark plug operation results in brown to grayish-tan deposits appearing on the portion of the plug that projects into the cylinder area. A small amount of red-brown, yellow, or white powdery deposit may also be present on the insulator tip around the center electrode. These deposits are normal combustion by-products of fuels and lubricants with additives. Some electrode wear is also normal.

Damaged plugs may seem to operate at idle. However, the plugs may fail on the road. Engines which are not running properly are often referred to as "misfiring." This means the ignition spark is not igniting the fuel-air mixture at the proper time. While other ignition and fuel system causes should be considered, the spark plugs may be reaching a ground by some other way besides jumping across the air gap at the tip of the plug, leaving the fuel-air mixture unburned. Misfiring may also occur when the tip of the spark plug becomes overheated and ignites the mixture before the spark jumps. This is referred to as "preignition." Should misfiring occur before the recommended change interval, locate and repair the cause.

Damaged plugs may cause any of the following symptoms:

Spark plug misfiring may be indicated in a number of ways:

Carbon fouling of the plugs is indicated by black carbon deposits, usually cause by frequent short trips where sufficient engine operating temperature is seldom reached. The following conditions are also often responsible for carbon fouling:

Oil fouling of the plug is indicated by wet oily deposits on the part of the plug in the cylinder, usually with little electrode wear. This may be caused by oil getting past worn piston rings. This condition may also occur during the break-in of a new or a newly-overhauled engine.

Deposit fouling occurs when the normal by-products of combustion build up enough to cause engine misfiring. In some cases, these deposits melt and form a shiny glaze on the insulator around the center electrode. If the fouling is found in only one or two cylinders, valve stem clearances or intake valve seals may be allowing excess lubricant to enter the cylinder, particularly if the deposits are heavier on the side of the plug that was facing the intake valve.

Excessive gap wear means that the airspace between the center and side electrodes at the bottom of the plug is too wide for constant plug firing. This may be due to improper gap adjustment or to excessive wear of the electrodes during vehicle operation. Refer to Section 0A for an inspection of the spark plug gap and gap size table. Excessive gap wear on low mileage plugs usually indicates one or more of the following:

1. The engine is operating at frequently higher speeds.
2. The engine often operates under higher loads.
3. The spark plug is too hot.

Loose plugs can become hot, causing electrode wear, a result of a combustion gases leaking past the threads. Lean fuel can also cause the wear. Excessive gap wear can also occur. The plug and cylinder head seats must be in good contact for proper heat transfer and plug cooling. Dirty or damaged threads in the head or on the plug can keep the plug from seating even though the plug is properly tightened. Overtightening may cause the plug shell to be stretched and can also result in poor contact between seats. In extreme cases, exhaust blow-by may occur.

Broken insulators are usually caused by one or more of the following conditions:

The broken insulator may only become obvious when oil or moisture penetrates the crack. The crack is usually just below the crimped area of the shell. Replace the spark plug if the insulator is damaged.

Heat shock breakage in the lower insulator tip generally occurs during severe loads or high operating speeds, and may be caused by over-advanced timing or low-grade fuels. Heat shock refers to a rapid increase in the tip temperature that causes the insulator material to crack.

Spark plugs with less than the recommended amount of service can sometimes be cleaned and regapped and returned to service. If there is any doubt about the serviceability of a plug, replace the plug.

Each spark plug boot covers a plug terminal and a portion of the insulator. The boots prevent flashover, which results in engine misfiring. Do not mistake corona discharge for flashover or a shorted insulator. Corona discharge is a blue light that shows up around the insulator shell crimp, often accompanied by a brown ring of dust. This is the visible evidence of a high tension field and has no effect on ignition performance. The dust is often mistaken for evidence of exhaust blow-by.