Table of Contents
Advertisement
IGNITION SYSTEM - SERVICE INFORMATION 8I - 25
ZH
PREIGNITION DAMAGE
Preignition damage is usually caused by excessive
combustion chamber temperature. The center elec-
trode (2) dissolves first and the ground electrode (1)
dissolves somewhat later. Insulators appear relatively
deposit free. Determine if the spark plug has the cor-
rect heat range rating for the engine. Determine if igni-
tion timing is over advanced or if other operating
conditions are causing engine overheating. (The heat
range rating refers to the operating temperature of a
particular type spark plug. Spark plugs are designed
to operate within specific temperature ranges. This
depends upon the thickness and length of the center
electrode's porcelain insulator.)
SPARK PLUG OVERHEATING
Overheating is indicated by a white or gray center
electrode insulator that also appears blistered. The
increase in electrode gap will be considerably in
excess of the normal 0.025 mm (.001 in.) per 3200 km
(2000 miles) of operation. This suggests that a plug
with a cooler heat range rating should be used. Over
advanced ignition timing, detonation and cooling sys-
tem malfunctions can also cause spark plug overheat-
ing (1).
Advertisement
Chapters
Table of Contents
