G 30 Van V8-454 7.4L VIN N TBI (1995)
Spark Plug: Description and Operation
DESCRIPTION
Resistor-type, tapered-seat spark plugs are used on this engine. No gasket is used on these spark plugs. Application and ID explain the letter
coding on these spark plugs. A dot before the spark plug code or the letter "C" after the number in the code indicates the spark plug has a copper
core. Refer to Specification / Mechanical or to the vehicle emissions control information label for correct gap information.
CONSTRUCTION
These spark plugs have a ceramic insulator that is approximately 6.35 mm (1/8 inch) longer than conventional spark plugs. The longer length spark
plugs magnify the problem of cracked insulators because most spark plug sockets are not of sufficient length to properly engage the shell hex. If
the spark plug shell hex is not fully engaged in the spark plug socket wrench, the socket may cause insulator cracking and/or breakage during plug
installation or removal.
OPERATION
When servicing these spark plugs, make sure the spark plug socket being used is deep enough to accommodate the longer length insulator. Use of
a spark plug socket that is NOT deep enough may result in the ceramic insulator becoming cracked above the spark plug shell.
Normal or average service is assumed to be a mixture of idling, low speed, and high speed operation with some of each making up the total daily
driving. Occasional or intermittent high-speed driving is essential to good spark plug performance. It provides increased and sustained combustion
heat that burns away excess deposits of carbon or oxide 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 that covers the spark plug terminal and extends
downward over a portion of the plug insulation These boots prevent flash-over with resultant missing of the engine.
Do not mistake corona discharge for flash-over or a shorted insulator. Corona discharge 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
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 insulator.
