Yanmar 6BY2 - Engine Knocks; Low Power Output; Engine Overheat

TROUBLESHOOTING
Troubleshooting Chart
13-8 BY Service Manual
© 2009 Yanmar Marine International
Engine Knocks
Low Power Output
Engine Overheat
Problem / Symptom Cause Action
Excess Fuel Injected
Defective fuel injector Check / replace fuel injector
High fuel injection pressure
Check / replace fuel pressure regulator /
sensor
Noise Changes with Engine Load
Incorrect or poor quality fuel Drain and refill tank
Worn crankshaft / bearings Repair as necessary
Broken piston / rings Repair as necessary
Problem / Symptom Cause Action
Miscellaneous
Clogged intake air filter Replace
Leaking cylinder head gasket Replace
Damaged turbocharger Replace
Incorrect propeller Replace
Excessive exhaust backpressure Remove obstruction
Fuel
Plugged fuel filter(s) Replace as necessary
Faulty fuel supply pump Replace
Low Fuel Injection Pressure
Defective fuel pressure regulator /
sensor
Check / replace
Worn high-pressure fuel pump Check / replace
Injection timing is incorrect ECU / software problem
Low RPM at Wide Open Throttle
Propeller pitch too great Replace
Engine overheated Reduce load / repair cooling system
Damaged turbocharger Replace
Problem / Symptom Cause Action
Instrument Shows High Temperature
Clogged seawater inlet Clean
Low coolant level Fill with coolant / inspect for leak
Clogged seawater filter (if equipped) Clean
Clogged hydraulic cooler Clean
Seawater pump worn or damaged Repair / replace as necessary
Defective sensor / instrument Repair as necessary
Defective thermostat Replace
Damaged closed coolant pump Replace
Combustion gas leakage (causes loss of
coolant)
Repair as necessary
Seawater pump belt slips or pump pulley
loose on pump shaft
Repair as necessary
Clogged heat exchanger Clean