Engine - Misfire Due to Carbon Tracking

NUMBER: 93-T-68

CORP.REF.NO: 376401

DATE: June 1993

SECTION: 6D4, 6E3, V6

SUBJECT:
ENGINE MISFIRE - CHANGE SPARK PLUG WIRE AND SPARK PLUG

MODELS/YEARS:
1992-93 EIGHTY EIGHT AND NINETY EIGHT W/3800 ENGINE (VINS L & 1)

CONDITION:





Some 1992-93 Eighty Eighty and Ninety Eight models with 3800 (L27 and L67-SC) engines 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 illustration). 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.