ENGINE MISFIRE (CHANGE SPARK PLUG WIRE & SPARK PLUG)

SUBJECT: ENGINE MISFIRE (CHANGE SPARK PLUG WIRE AND SPARK PLUG)

VEHICLES AFFECTED: 1992-93 "C AND H" CARS W/3800 (L27/L67) ENGINE (VINS L/1)

CONDITION:

--------- Some 1992-93 model year C and H cars with 3800 (L27 and L67) supercharged engines (VINs L and 1) may exhibit a misfire condition due to carbon tracking at the spark plug to spark plug boot interface. Carbon tracking leaves dark lines (possibly looking like cracks) permanently etched into the spark plug ceramic and rubber of the boot (see Figure 1). Carbon tracking cannot be rubbed or cleaned off by any means.

CAUSE:

----- Higher peak cylinder pressures require higher demand voltage for spark plug operation. Higher demand voltage increases the stress on the spark plug to spark plug boot dielectric interface, such that contamination and air gaps between the spark plug and boot can cause this interface to breakdown. A break in the dielectric interface can allow the spark to find a path to ground other than the center electrode. These paths or carbon tracks are etched into both the spark plug and the spark plug boot.

CORRECTION:

---------- To correct this condition, it is necessary to change both the spark plug wire and the spark plug at the same time on only the cylinder involved. Changing only the spark plug or only the spark plug wire will not prevent the carbon tracking from recurring. Carbon tracking will happen again in the same location much quicker if half of the track is still available. Recurrence of the same problem is likely in as little as 1,000 miles if the carbon track is not totally removed.

General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.