• Overheated spark plug electrodes (improper heat range or defective plug).
• Inadequate engine cooling.
4. Inspect the piston for damage caused by detonation (knock).
Typical detonation damage
a - Controlled ignition spark
b - Combustion begins
c - Continued combustion
d - Detonation occurs
NOTE: The use of poor quality, contaminated, or incorrect fuels will cause poor performance and engine damage.
5. If indicated, inspect the engine for causes of detonation damage to pistons:
• Use of low octane gasoline or neglecting engine maintenance
• Lean fuel mixture at or near full throttle (could be caused by leaking intake manifold)
• Cross‑firing ignition system
• The accumulation of deposits on the piston and/or combustion chamber that result in a higher compression ratio
• Inadequate engine cooling
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.
Starter Motor Will Not Crank Engine, or Cranks Slowly
Possible Cause
Remedy
Battery switch turned off. Turn the switch on.
Remote control not in neutral position. Position the control lever in neutral.
Open circuit breaker or fuse.
Check and reset the main power circuit breaker or replace the fuse. Check the 5‑amp
fuse on the power harness connected to the battery, and replace if necessary. Inspect
the corresponding circuit to determine the cause of failure.
Loose or dirty electrical connections or
damaged wiring.
Check all electrical connections and wires (especially battery cables). Clean and tighten
all faulty connections.
Bad battery or low battery voltage. Test the battery and charge if necessary; replace if bad.
Lanyard stop switch activated. Check the lanyard stop switch.
Engine Troubleshooting
90-8M0099748 eng DECEMBER 2015 © 2016 Mercury Marine Page 3C-9
To Next Page
Loading...
Need help?
General
