Pre-Ignition Damage
Splashed Deposits
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 lu-
brication.
Spotted deposits, which sometimes occur after long
delayed tune-up, accumulate after a long period of
misfiring. When normal combustion temperatures
are restored, upon installation of new plugs, deposits
loosen from top of piston and head and are thrown
against hot insulator. Clean and service plugs and re-
install.
72423
72422
Mechanical Damage
Reversed Coil Polarity
Mechanical damage to spark plug firing end is
caused by foreign object in combustion chamber.Be-
cause of valve overlap, small objects can travel from
one cylinder to another. Check all cylinders, intake
manifold and exhaust material to prevent further
damage.
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.
72423
72422
IMPORTANT: When working on engine, spark
plug holes and carburetor throat should be kept
covered to prevent foreign objects from entering
combustion chamber.
Index
1C-4 - TROUBLESHOOTING
90-823224--2 796
| Categories | Mercury MerCruiser Manuals |
|---|---|
| Tags | Mercury MerCruiser 454 CID, Mercury MerCruiser 502 CID |
| Model Year | 1993, 1994, 1995, 1996, 1997 |
| Download File |
|
| Document File Type | |
| Copyright | Attribution Non-commercial |
(4 votes, average: 4.5 out of 5)
Marine readers have rated 1993 1997 Mercury-MerCruiser GM V8 454 CID 7.4L and 502 CID 8.2L Marine Engines Service Manual Number 16 4.5 out of 5.0 based on 4 product reviews. Hugely helpful service manual! Perfect. Thank you!
Manuals are all Important for Technician
This book is invaluable if you do your own repairs. Great book.
Could not find a copy until a search brought me here.
Excellent print.
Thank you