COUPLING AS 4980785 - Caterpillar

Probable Causes
Cold Mode
Engine in cold mode (if applicable)Throttle Signal
Intermittent throttle signalInjection Actuation Pressure
Engine oil level
Proper operation of the injection actuation pressure control valveElectrical Connectors
Inspect electrical connectors.Fuel
Fuel supply
Injector misfiringAir Inlet and Exhaust System
Restriction in the air inlet and exhaust systemRecommended Actions
Note: If the problem only occurs under certain conditions, test the engine under those conditions. Examples of certain conditions are high engine speed, full load and engine operating temperature. Troubleshooting the symptoms under other conditions can give misleading results.Engine in Cold Mode (if applicable)
Use Cat ET to verify that the engine has exited cold mode. Cold mode operation may cause the engine to run rough and engine power may be limited.Intermittent Throttle Signal
Monitor the status for "Throttle Position" on Cat ET. Verify that the status for "Throttle Position" is stable and that the engine is able to reach high idle speed. Refer to Troubleshooting, "Speed Control (Switch) - Test".Engine Oil Level
Check the engine oil level. Engine oil supplies the injection actuation pressure circuit. The engine oil must be kept at the proper level for fuel injection.Proper Operation of the Injection Actuation Pressure Control Valve
Check the operation of the injection actuation pressure control valve. Refer to Troubleshooting, "Injection Actuation Pressure Control Valve - Test".
Check the injection actuation pressure. Refer to Troubleshooting, "Injection Actuation Pressure Control Valve - Test".Inspect Electrical Connectors
Disconnect the J1/P1 and J2/P2 ECM connectors. Inspect each connector for moisture and corrosion. Also, inspect the harness and connectors for the unit injectors from the ECM to the valve cover. Inspect the connectors for the engine speed/timing circuit. Refer to Troubleshooting, "Electrical Connectors - Inspect".Fuel Supply
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.
Ensure that the fuel supply valve (if equipped) is in the full OPEN position.
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.
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 injectorsNote: A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel. Refer to Systems Operation/Testing and Adjusting.
Check the fuel tank for foreign objects which may block the fuel supply.
Check the fuel filters.
Check the diesel fuel for contamination. Refer to Systems Operation/Testing and Adjusting.
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.Injector Misfiring
Use Cat ET to perform the injector solenoid test 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 check the performance of each cylinder. Refer