Spark Plug: Description and Operation

Resistor type, copper core, tapered seat quantum spark plugs are used on all engines. No gasket is used on these tapered seat plugs. A dot before the spark plug code or the letter C after the number in the code indicates that the plug has a copper core. For the correct gap information refer to the Vehicle Emissions Control Information label under the hood or refer to SPECIFICATIONS/ELECTRICAL AND ELECTRONIC SPECIFICATIONS.

Normal or average service is assumed to be a mixture of idling, slow speed, and high speed operation with some of each making up the daily total driving. Occasional or intermittent high-speed driving is essential to good spark plug performance as it provides increased and sustained combustion heat that burns away any excess deposits or carbon or oxides that may have accumulated from frequent idling or continual stop and go or slow speed driving. Spark plugs are protected by an insulating boot made of special heat-resistant material which covers the spark plug terminal and extends over a portion of the plug insulator. These boots prevent flash-over with resultant missing of the engine, even though a film is allowed to accumulate on the exposed portion of the plug porcelains.

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 a high-tension field, and has no effect on ignition performance. Usually it can be detected only in the darkness. This discharge may repel dust particles, leaving a clear ring on the insulator just above the shell. This ring is sometimes mistakenly regarded as evidence that combustion gases have blown out between the shell and the insulator.