Spark Plug: Description and Operation

The spark plugs are the resistor type with a tapered seat and are used on L36 and L67 engines. No gasket is used on these tapered seat plugs. Always use a 6 point deep socket (with rubber insert) in good condition when replacing spark plugs. when setting the gap on a spark plug, use a wire type feeler gage and make the gap adjustment by bending the ground side; electrode.

The spark plugs have platinum pads welded to he electrodes. These pads extend the spark plug life to 60,000 kilometers (100,000 miles).

The spark plugs can be identified by the "ribless" porcelain insulator. This "ribless" insulator and boot design provide a better plug-to-boot retention. The spark plug and boot design significantly reduces carbon tracking and reduces engine misfire.

Worn, cracked or dirty plugs may give satisfactory operation at idling speed, but under operating conditions they frequently fail. Faulty plugs re indicated in a number of ways: poor fuel economy, power loss, loss of speed, hesitation, shudder, medium medium intake manifold backfire, hard starting and general poor engine performance.

Fouled plugs may be indicated by black carbon posits. The black deposits are usually the result of low-speed driving and short runs where sufficient engine operating temperature is seldom reached. Worn pistons, rings, faulty ignition, over-rich fuel mixture or old spark plugs may result in carbon deposits.

Excessive gap wear on plugs of low mileage, usually indicates the engine is operating at high speeds or loads that are consistently greater than normal or that a plug which is too hot is being used. Electrode wear may also be the result of plug overheating, caused by combustion gases leaking past the threads, due to insufficient torqueing of the spark plug. Excessively lean fuel mixture will also result in excessive electrode wear.

Broken insulators are usually the result of improper installation or carelessness when re-gapping the plug. Broken upper insulators usually result from a poor fitting wrench or an outside blow. The cracked insulator may not show up right away but will as soon oil or moisture penetrates the crack. The crack is usually just below the crimped part of shell and may not be visible.

Broken lower insulators usually result from carelessness when re-gapping and generally are visible. This type of break may result from the plug operating "Hot", which may happen in periods of high-speed operation or under heavy loads. When gapping a spark plug, always make the gap adjustment by bending the ground (side) electrode. Spark plugs with broken insulators should always be replaced.

Each spark plug boot covers the spark plug terminal and a portion of the plug insulator. These boots prevent flash-over which causes engine misfiring. Do not mistake corona discharge for flash-over or a shorted insulator. Corona is a steady blue light appearing around the insulator, just above the shell crimp. It is the visible evidence of high-tension field and has no effect on ignition performance. Usually it can be dust particles leaving a brown ring on the insulator just above the shell. This ring is sometimes mistakenly regarded as evidence that combustion gases have blown out between shell and insulator.