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The chart below shows the most common questions asked by owners of Detroit Diesel® engines 12V149 Natural when trying to troubleshoot why their engines underperform.  It categorizes areas of possible malfunction, likely cause and recommended action to bring your new, rebuilt or used  Detroit Diesel® engine back to proper operation.  The chart will give you confidence when speaking with your Detroit Diesel® engine mechanic or ordering parts.  As a quick reference guide only, the chart must not be thought of as a substitute for the use of your Detroit Diesel® engine 12V149 Natural Owner's operating or service manual.

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PROBLEM

POSSIBLE REASON

CHECK
Engine will not start Lack of air intake or restricted air intake √
Broken blower shaft  
Worn out blower shaft  
Defective fuel pump  
Defective starter  
Discharged battery  
High exhaust back pressure  
Black smoke coming out of engine Defective injector  
Contaminated fuel  
Broken or worn cylinder parts  
Engine overloaded  
Faulty intercooler or aftercooler (for turbo engines only)  
White smoke coming out of engine Broken piston ring  
Incorrectly installed ring set  
Defective injector  
Fuel quality or grade  
Long idle periods  
Broken or bent push rod  
Injector or governor improperly adjusted  
Low engine oil pressure Water in engine oil pan  
Fuel in engine oil pan  
Defective oil cooler  
Engine overloaded  
Crankcase overfilled  
Low engine RPM Improperly working injector  
Governor calibration  
Hi engine RPM Governor calibration  
Engine overheating Defective fresh water pump  
Defective raw water pump (marine engines only)  
Defective thermostat or thermostat seal  
Clogged radiator or heat exchanger (marine engine only)  
Grey smoke coming out of engine Long idle periods  
Defective intercooler or aftercooler (for turbo engine only)  
Restricted air intake  
Defective injector  
Contaminated fuel  
Blower or turbocharger seals leaking  
Geartrain makes noises Low oil level  
Engine driven accesories  
Damage main or rod bearing  
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