C-10, C-12, C-15 and C-16 Industrial Engines – Engine Misfires, Runs Rough or Is Unstable

Note: If the symptom is intermittent and the symptom cannot be repeated, refer to Troubleshooting, “Intermittent Low Power or Power Cutout”. If the symptom is consistent and the symptom can be repeated, continue with this procedure.

Probable Causes

  • Diagnostic codes

  • Programmable parameters

  • Electrical connectors

  • Cold mode

  • Throttle signal

  • Unit injectors

  • Fuel supply

  • Air inlet and exhaust system

Recommended Actions

Note: If the symptom only occurs under certain operating conditions (high idle, full load, engine operating temperature, etc), test the engine under those conditions. Troubleshooting the symptom under other conditions can give misleading results.

Diagnostic Codes

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

Programmable Parameters

Check the following parameters on Cat ET:

  • Throttle Position Sensor

  • Direct Fuel Control Mode

Determine the type of throttle that is used in the application. Program the parameters to match the type of throttle that is used. Refer to Troubleshooting, “Throttle Position Sensor Circuit – Test” for more information.

Note: The engine will have poor performance if the parameters are not programmed correctly.

Electrical Connectors

Check the connectors for the Electronic Control Module (ECM) and the connectors for the unit injectors for correct installation. Refer to Troubleshooting, “Electrical Connectors – Inspect”.

Cold Mode

Use Cat ET to verify that the engine has exited cold mode. Cold mode operation may cause the engine to run rough and the engine power may be limited.

Throttle Signal

Monitor the throttle signal on Cat ET. Verify that the throttle signal is stable from the low idle position to the high idle position.

Unit Injectors

  1. Use Cat ET to determine if there are any active diagnostic codes for the unit injectors.
  1. Perform the injector solenoid test on Cat ET in order to determine if all of the injector solenoids are being energized by the ECM. Refer to Troubleshooting, “Injector Solenoid Circuit – Test” for the proper procedure.
  1. Perform the cylinder cutout test on Cat ET in order to identify any injectors that might be misfiring. Refer to Troubleshooting, “Injector Solenoid Circuit – Test” for the proper procedure.

Fuel Supply

  1. Check the fuel lines for the following problems: restrictions, collapsed lines and pinched lines. If problems are found with the fuel lines, repair the lines and/or replace the lines.
  1. Check the fuel tank for foreign objects which may block the fuel supply.
  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.

  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.
  1. Check the fuel pressure during engine cranking. Check the fuel pressure after the fuel filter. Refer to Systems Operation/Testing and Adjusting, “Fuel System” for the correct pressure values. If the fuel pressure is low, replace the fuel filters. If the fuel pressure is still low, check the following items: fuel transfer pump, fuel transfer pump coupling and fuel pressure regulating valve.

Air Inlet and Exhaust System

  1. Check for an air filter restriction. Clean plugged air filters or replace plugged air filters. Refer to the Operation and Maintenance Manual for additional information.
  1. Check the air inlet and exhaust system for restrictions and/or for leaks. Refer to Systems Operation/Testing and Adjusting, “Air Inlet and Exhaust System”.