TROUBLESHOOTING
SERVICE MANUAL NUMBER 23
Page 1C-5
90-861326--1 MARCH 1999
Cold Fouling
Dry, black deposits indicate rich fuel mixture or weak ignition. Clogged flame arrestor or
weak ignition components all are probable causes. If, however, only one or two plugs in set
are fouled, check for sticking valves or bad ignition leads. After correcting cause, service
(clean, file and re-gap) plugs and reinstall.
72421
Overheating
Insulator is dull white or gray and appears blistered. Electrodes are eroded and there is an
absence of deposits. Check that correct plug heat range is being used. Also check for
over-advanced ignition timing, cooling system malfunction, lean fuel/air mixtures, leaking
intake manifold or sticking valves. Replace spark plugs.
72421
High Speed Glazing
Insulator has yellowish, varnish-like color, indicating that temperatures suddenly have risen,
usually during hard, fast acceleration under heavy load. Normal deposits do not get a
chance to blow off. Instead, they melt and form a conductive coating. Replace spark plugs.
If condition recurs, use colder heat range plug and service plugs more frequently.
72421
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