TROUBLESHOOTING SERVICE MANUAL NUMBER 23
Page 1C-6
90-861326--1 MARCH 1999
Scavenger Deposits
Powdery white or yellow deposits are built up on shell, insulator and electrodes. This is
normal appearance with certain branded fuels. Accumulation on ground electrodes and
shell areas may be unusually heavy, but may be easily chipped off. Plugs can be serviced
(clean, file and re-gap) and reinstalled.
72422
Pre-Ignition Damage
Pre-ignition damage is caused by excessive high temperatures. Center electrode melts
first, followed by ground electrode. Normally, insulators are white but may be dirty if plug has
been misfiring. Check for correct plug heat range, advanced ignition timing, lean fuel
mixture, incorrect fuel used, malfunctioning cooling system, leaking intake manifold or lack
of lubrication. Replace spark plugs.
72422
Reversed Coil Polarity
Concave erosion of ground electrode is an indication of reversed polarity. Center electrode
will show only normal wear. Engine will misfire and idle rough. To correct, reverse primary
coil leads. Replace spark plugs.
72422
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