3500B Engines for 5130B and 5230B Excavators Engine Misfires, Runs Rough or Is Unstable Caterpillar


Engine Misfires, Runs Rough or Is Unstable
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Note: If the symptom cannot be repeated, refer to Troubleshooting, "Low Power/Poor or No Response to Throttle". If the symptom can be repeated, continue with this procedure.

The probable root causes are listed in order below:

  • Cold Mode Operation

  • Throttle signal

  • Electrical connector

  • Injector solenoid

  • Fuel supply

  • Air inlet restrictions

  • Exhaust restrictions

Note the conditions that caused the problem. Troubleshooting the symptoms under other conditions can give misleading results.

Perform the following tests in order:

  1. Use the ET in order to verify that the engine has exited cold mode. During Cold Mode, injection timing is modified. The cylinders may cut out. Cold mode cylinder cutouts may cause variations in vibration and available power. This is normal operation.

    1. Use the ET in order to monitor the temperature of the coolant. If the reading is incorrect, refer to Troubleshooting, "Engine Sensor Open/Short Test".

  1. Use the ET in order to monitor the status of the throttle signal. Observe the throttle position. The throttle position should be stable. The throttle position should reach 100 percent. Refer to Troubleshooting, "Throttle Switch".

  1. Check for correct installation of the ECM connector J2/P2 and Fuel Injector connector J4/P4 through J19/P19. Refer to Troubleshooting, "Inspecting Electrical Connectors".

  1. Use the ET to determine if any active diagnostic codes are present for the Injector Solenoids. Use the ET to determine if any logged diagnostic codes are present for the Injector Solenoids. Perform the Injector Solenoid Test. Observe that the Injector Solenoids are being energized on the ET. Perform the Cylinder Cutout Test. Locate the misfiring cylinder. Refer to Troubleshooting, "Injector Solenoids".

  1. Check fuel lines for the following problems: restrictions, collapse and pinched line. Repair the lines and/or replace the lines. Refer to the Systems Operation, "Fuel System".

    1. Check the fuel tank for foreign objects which may block the fuel supply. Check for air in the low pressure fuel supply system after you perform the following procedures:

      • Replacing the fuel filters

      • Working on the low pressure fuel supply circuit

      • Replacing fuel injectors

    1. Purge air from the low pressure fuel supply circuit with the hand priming pump and by cranking the engine in 30 second cycles. After you crank the engine, stop for two minutes. This will allow the starting motor to cool. Loosen the vent plug at the fuel return. The plug is located on the rear upper left side of the engine block. Hand prime the engine again if air in fuel continues. A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel.

    1. Check fuel quality. In temperatures below 0 °C (32 °F), check for solidified fuel (wax). Refer to Special Instruction, SEBD0717, "Diesel Fuels And Your Engine". Check the fuel pressure while the engine is cranking. Check the fuel pressure at the filter. Refer to the Specifications manual for correct pressure values. If the pressure is low, check for plugged 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. Check for a problem with the combustion system.

  1. Check for restrictions in the air inlet system. Refer to the Systems Operation.

  1. Check for restrictions in the exhaust system. Refer to the Systems Operation.

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