
Mechanical Damage
Mechanical damage to the spark plug firing end is caused by a foreign object in the combustion chamber. Because of valve
overlap, small objects can travel from one cylinder to another. Check all cylinders, the intake manifold, and the exhaust material
to prevent further damage. Replace the spark plugs.
27654
IMPORTANT: When working on the engine, the spark plug holes, the intake, and the throttle body should be kept covered to
prevent foreign objects from entering the combustion chamber.
Piston Inspection
1. Replace pistons that are damaged or show signs of excessive wear.
2. Inspect the piston for damage caused by preignition.
14394
Typical preignition damage
a -
Preignition begins
b -
Controlled ignition spark
c -
Remaining fuel ignition
d -
Flame front collision
NOTE: Engine failures that result from these conditions are beyond the control of Mercury MerCruiser. No warranty will
apply to failures that occur under these conditions.
3. If indicated, inspect the engine for causes of preignition damage to pistons:
•
Combustion chamber hot spots caused by damaged components, foreign material, or combustion chamber deposits.
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a
b
c
d
Engine Troubleshooting
Page 3C-8
© 2016 Mercury Marine
90-8M0099748 eng DECEMBER 2015
Summary of Contents for MERCRUISER
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Page 6: ...90 8M0099748 eng DECEMBER 2015 2016 Mercury Marine Page iv...
Page 12: ...General Information Notes Page 1A 6 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 70: ...Maintenance Notes Page 1C 54 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 96: ...Troubleshooting Notes Page 1D 26 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 156: ...Installation Notes Page 2B 52 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 202: ...Engine Disassembly Notes Page 3A 46 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 286: ...Engine Troubleshooting Notes Page 3C 14 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 314: ...Waste Spark System Notes Page 4B 8 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 330: ...Charging System Notes Page 4C 16 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 404: ...MPI ECT Fuel System Notes Page 5A 34 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 424: ...All Models Notes Page 6A 20 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 448: ...Models with Closed Cooling Notes Page 6C 20 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 462: ...Water Flow Diagrams Notes Page 6D 14 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 474: ...Important Information Notes Page 7A 12 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 477: ...Manifolds and Elbows Notes 90 8M0099748 eng DECEMBER 2015 2016 Mercury Marine Page 7B 3...
Page 538: ...Compact Hydraulic Steering Notes Page 8B 12 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 558: ...Notes Color Diagrams Page 10A 2 2016 Mercury Marine 90 8M0099748 eng DECEMBER 2015...
Page 559: ...Notes Color Diagrams 90 8M0099748 eng DECEMBER 2015 2016 Mercury Marine Page 10A 3...
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