Engine Runs Poorly At High Rpm; Engine Acceleration Is Poor - Mercury MerCruiser MCM 454 Mag MPI Service Manual

TROUBLESHOOTING

Engine Runs Poorly At High RPM

Crankcase overfilled with oil
Anti-siphon valve (if equipped)
Plugged fuel tank vent
Fuel supply
Ignition timing
Low grade of fuel or water in the fuel
Spark plugs
Spark plug wires
Distributor cap or rotor
Coil
Distributor
Engine overheating
Low compression
Restricted exhaust

Engine Acceleration Is Poor

Idle mixture screws
Incorrect ignition timing
Incorrect distributor or amplifier advance
curve
Cracked or dirty distributor cap or rotor
Vacuum leak
Spark plugs
Low compression
Index Index
Page 1C-14
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Cause
Also refer to "Poor Boat Performance"
Cause
Also refer to "Poor Boat Performance"
SERVICE MANUAL NUMBER 23
Special Information
Check oil level with boat at rest in the
water.
Restricting fuel supply
Refer to "Fuel Injection Troubleshooting,"
SECTION 5D
Fouled, burned, cracked porcelain,
incorrect heat range
Poor insulation, broken wires
Dirty or cracked
Excessive play in shaft
Refer to "Engine Overheats"
Worn valves, rings, cylinders, etc.
Special Instructions
Refer to SECTION 4B
Intake manifold
Fouled, burned; wrong heat range;
cracked porcelain
90-861326--1 MARCH 1999