C 3500 Truck 2WD V8-454 7.4L (1990)
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Spark Plug Wire: Customer Interest
Engine - Miss, Hesitation, or Roughness
Number: 93-35-6D
Section: 6D
Date: OCT. 1992
Corporate Bulletin No.: 716404R
ASE No.: A1, A8
Subject:
ENGINE MISS HESITATION OR ROUGHNESS DUE TO PIERCED SECONDARY IGNITION COMPONENTS
Model and Year:
1980-93 ALL PASSENGER CARS AND TRUCKS
THIS BULLETIN CANCELS AND SUPERSEDES DEALER SERVICE BULLETIN NO. 87-121, DATED MAY 1987. THE 1989-93 MODEL
YEARS HAVE BEEN ADDED. ALL COPIES OF 87-121 SHOULD BE DISCARDED.
During the diagnosis procedure for an engine miss, hesitation or roughness, a spark plug or spark plug wire condition may be suspected. Several types of
commercial or homemade diagnostic equipment required the secondary ignition boots or wire to be pierced. This is normally done to check for spark
plug firing or to perform a cylinder balance test. Similarly the use of pliers or other such tools to disengage a spark plug boot may pierce or damage the
boot or wire. Secondary ignition components should not be pierced for any reason.
Piercing a spark plug wire and/or distributor boot may create a condition that will not be immediately apparent. Over time, the hole in the pierced boot
may allow a ground path to develop creating a plug misfire condition. Heavily moisture laden air in the vicinity of the pierced boot may accelerate this
effect.
Piercing a secondary ignition wire creates a gap in the wire's conductive core. This gap is a point of high resistance. The current flow in the wire will
increase to compensate for the higher wire resistance. Over time, the wire may fail creating a plug misfire condition. The time required for the condition
to appear depends upon the extent of damage to the conductive core.
To help prevent future condition that are spark plug wire related, do not pierce or otherwise damage any secondary ignition component. Only use
diagnostic equipment containing an inductive pick-up to check for spark plug firing or to perform cylinder balance tests. When disengaging a spark plug
boot from the spark plug, twist the flanged boot 1/2 turn then pull on the boot only to remove the wire.