C-10 and C-15 Petroleum Engines Caterpillar

Engine Misfires, Runs Rough or Is Unstable

Usage:

C-10 Z2B

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The connection of any electrical equipment and the disconnection of any electrical equipment may cause an explosion hazard which may result in injury or death. Do not connect any electrical equipment or disconnect any electrical equipment in an explosive atmosphere.

Note: If the symptom is intermittent and the symptom cannot be repeated, refer to the diagnostic procedure 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"
"Desired Speed Input Configuration"
"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 the diagnostic functional test Troubleshooting, "Throttle Position Sensor Circuit - Test" for more information.

Note: If the parameters are not programmed correctly, then the engine will have poor performance.

Electrical Connectors

Check for the correct installation of the J1/P1 and J2/P2 connectors for the Electronic Control Module (ECM). Check the unit injector connectors. Refer to the diagnostic functional test 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 throttle signal on Cat ET. Verify that the throttle signal is stable from the low idle position to the high idle position.

Unit Injectors

Use Cat ET to determine if there are any active diagnostic codes for the unit injectors.

Perform the Injector Solenoid Test on Cat ET in order to determine if all of the injector solenoids are being energized by the ECM.

Perform the Cylinder Cutout Test on Cat ET in order to identify any misfiring cylinder(s). Refer to Troubleshooting, "Injector Solenoid Circuit - Test" for information.

Fuel Supply

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.

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

Check for air in the low pressure fuel supply 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

Purge air from the low pressure fuel supply circuit. Refer to Operation and Maintenance Manual, "Fuel System - Prime" for the complete procedure.
Note: A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel.

Check fuel quality. In temperatures below 0 °C (32 °F), check for solidified fuel (wax). Refer to Operation and Maintenance Manual for information on cold weather operation.

Check the fuel pressure during engine cranking. Check the fuel pressure after the fuel filter. Refer to Systems Operation/Testing and Adjusting, "Fuel System Pressure - Test" 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.