3176C, 3406E and 3456 Industrial Engines Troubleshooting – Engine Misfires, Runs Rough or Is Unstable

The probable root causes are listed in order below:

Note: If the problem is intermittent and the problem cannot be duplicated, refer to Troubleshooting, “Power Is Intermittently Low or Power Cutout Is Intermittent”.

Note: If the problem only occurs under certain conditions, test the engine under those conditions. Examples of certain conditions are high rpm, full load and engine operating temperature. Troubleshooting the symptoms under other conditions can give misleading results.

Probable Causes


  • Diagnostic codes 
  • Fuel supply 
  • Cold mode operation and cold cylinder cutout 
  • Throttle 
  • Air intake and exhaust system 
  • Electronic unit injectors 
  • Cylinder performance 

Recommended Actions

Diagnostic Codes

Check for active diagnostic codes on Caterpillar Electronic Technician (ET). Troubleshoot any active codes before continuing with this procedure.

Fuel Supply


  1. Visually check the fuel level. Do not rely on the fuel gauge only. If necessary, add fuel. If the engine has been run out of fuel, it will be necessary to purge the air from the fuel system. Refer to Operation and Maintenance Manual for more information.


  1. Ensure that the fuel supply valve (if equipped) is in the full OPEN position.


  1. Check the fuel lines for the following problems: restrictions, collapsed lines, pinched lines and loose connections. If problems are found with the fuel lines, repair the lines and/or replace the lines.


  1. Prime the fuel system if any of the following procedures have been performed: 
    • Replacement of the fuel filters 
    • Service on the low pressure fuel supply circuit 
    • Replacement of unit injectors 

    Note: A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel. Refer to Systems Operation/Testing and Adjusting.


  1. Check the fuel tank for foreign objects which may block the fuel supply.


  1. Check the fuel filters.


  1. Check the diesel fuel for contamination. Refer to Systems Operation/Testing and Adjusting.


  1. Cold weather adversely affects the characteristics of the fuel. Refer to the Operation and Maintenance Manual for information on improving the characteristics of the fuel during cold weather operation.

Cold Mode Operation and Cold Cylinder Cutout

Use Cat ET in order to verify that the engine has exited cold mode. During cold mode, fuel injection timing is modified. When the engine is in cold mode, the cold cylinder cutout strategy may be active. Cold mode cylinder cutouts may cause variations in vibration and available power. This is normal operation.


There may be a problem with the throttle. Refer to Troubleshooting, “Speed Control – Test”.

Air Intake and Exhaust System


  1. Check the air filter restriction indicator, if equipped. Clean plugged air filters or replace plugged air filters. Refer to the Operation and Maintenance Manual.


  1. Check the air inlet and exhaust system for restrictions and/or leaks. Refer to Systems Operation/Testing and Adjusting.

Electronic Unit Injectors or Cylinder Performance


  1. Check the valve lash and reset the valve lash, if necessary. Refer to Systems Operation/Testing and Adjusting.


  1. Check for correct installation of the unit injector connectors. Check for correct installation of all other applicable connectors. Refer to Troubleshooting, “Electrical Connectors – Inspect”.


  1. Perform the “Injector Solenoid Test” on Cat ET in order to determine if all of the injector solenoids are being energized by the Electronic Control Module (ECM).


  1. Perform the “Cylinder Cutout Test” on Cat ET in order to identify any injectors that might be misfiring.


  1. If Cat ET indicates a problem, remove the electronic unit injector from the suspect cylinder and install a new electronic unit injector. Refer to Disassembly and Assembly.


  1. Possible causes of low compression are shown in the following list: 
    • Faulty piston 
    • Faulty piston rings 
    • Worn cylinder bores 
    • Worn valves 
    • Faulty cylinder head gasket 
    • Damaged cylinder head 


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