- Cold cylinder
- Electrical connectors or power supply
- Ignition system
- Incorrect base timing
- Fuel supply
- Incorrect air/fuel ratio
- Incorrect governor adjustment
- Compressor bypass valve
- Air inlet restriction
- Exhaust restriction
- Binding of the throttle actuator
- Incorrect valve lash
- Cylinder head and related components
Note: If the symptom only occurs under certain operating conditions (high idle, full load, engine operating temperature, etc), test the engine under the conditions. Troubleshooting the symptom under other conditions can give misleading results.
The Caterpillar Electronic Technician (ET) and the Integrated Temperature Sensing Module (ITSM) can be used to detect a misfiring cylinder. Use the following procedure:
- Use the "Data Link/Select ECM" option on the Cat ET to select the ITSM.
- Select "Diagnostics/Diagnostic Tests".
- Select the suspect cylinder and click the "Start" button in the lower left corner of the screen.
Cat ET will display a graph of the cylinder's exhaust gas temperature. The output voltage of the transformer's secondary circuit, the engine speed, and the desired engine speed are also displayed.
Locate the misfiring cylinder. Check the following components for failure: spark plug, extender, ignition transformer and primary wiring. Inspect the extender for signs of pin holes and/or of arcing.
Refer to Troubleshooting, "Ignition Transformers Secondary Circuit and Spark Plugs".
Electrical Connectors or Power Supply
There may be an intermittent interruption of power. Check the wiring harnesses and the connectors. Inspect the connectors in the terminal boxes. Inspect the power supply connections and the ground.
Inspect the wiring from the power supply to the control modules. Refer to Troubleshooting, "Electrical Power Supply".
Inspect the ignition transformers for the following conditions: loose connections, moisture, short circuits and open circuits. Inspect the primary wiring and the secondary electrical connections.
Make sure that the correct transformers and spark plugs are installed. Inspect the extenders for signs of pin holes and of arcing.
Maintain the spark plug according to the engine's Operation and Maintenance Manual.
Verify that the base timing is correct. Refer to Systems Operation/Testing and Adjusting, "Ignition Timing - Adjust".
Make sure that fuel is supplied at a sufficient pressure that is stable. Make sure that the size of the fuel line is sufficient. Inspect the fuel system for leaks.
The following conditions can cause the engine to malfunction:
- Low fuel pressure
- High fuel pressure
- Poor fuel quality
Make sure that the fuel pressure is correct. When possible, interview the operator in order to determine if fuel quality is in question. Try to determine if the source of the fuel was changed.
Inspect the fuel system components: fuel filter, gas pressure regulator, gas shutoff valve and fuel metering valve. Verify that the system's components are operating correctly.
Replace the fuel filter, if necessary.
An air/fuel mixture that is too rich or too lean will have an adverse effect on engine operation. Verify that the exhaust emissions are correct. Refer to Systems Operation/Testing and Adjusting, "Air/Fuel Ratio Control - Adjust (Oxygen Feedback)" or Systems Operation/Testing and Adjusting, "Air/Fuel Ratio Control - Adjust (Charge Density)".
A change in the fuel energy content will change the air/fuel ratio. Obtain a fuel analysis.
The fuel supply pressure must be adequate and stable.
The governor's parameters must be programmed with the values that provide stable operation. Refer to Systems Operation/Testing and Adjusting, "Engine Governing - Adjust".
The actuator for the compressor bypass valve must be installed properly in order to provide stable operation. Refer to Disassembly and Assembly, "Actuator Bypass Valve (Variable) - Install".
The maximum allowable air inlet restriction is 3.75 kPa (15 inches of H2O). If the indication is higher than the maximum permissible restriction, clean the filter element or install a new filter element. Check the restriction again. If the restriction remains too high, inspect the air inlet piping for obstructions.
For more information, refer to Systems Operation/Testing and Adjusting, "Restriction of Air Inlet and Exhaust".
Measure the exhaust restriction during engine operation with a load. For data that is specific to the engine, refer to the engine's Technical Marketing Information.
Investigate the cause of the exhaust restriction. Perform adjustments and/or make repairs, as needed.
Check for Binding of the Throttle Actuator
Set the engine control to the OFF/RESET mode. Remove the electrical power from the engine. Move the throttle plate while you feel the motion. If the motion is sticky and/or rough, investigate the cause of the binding. Make the necessary repairs.
Check the valve lash. Refer to Systems Operation, Testing And Adjusting, "Valve Lash and Valve Bridge Adjustment".
Cylinder Head and Related Components
Measure the cylinder compression. Refer to the engine's Operation and Maintenance Manual, "Cylinder Pressure - Measure/Record".
Inspect the components of the valve train for good condition. Check for signs of damage and/or of wear to the valves, cylinder head gasket, etc. Inspect the condition of the camshafts. If a camshaft is replaced, new valve lifters must be installed.