0345586 JOHNSON GROMMET ASSY.

Probable Causes
Diagnostic codes
Electrical connectors
Cold mode
Decelerator position sensor
Unit injectors
Fuel supply
Air inlet and exhaust system
Incorrect torque convertor speed output sensor signalRecommended 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 (Cat® ET). Troubleshoot any active codes before continuing with this procedure.Electrical Connectors
Check for correct installation of the J1/P1 and J2/P2 Electronic Control Module (ECM) connectors and the unit injector connectors. 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.Decelerator Position Sensor
Monitor the signal for the decelerator position sensor on Cat® ET. Verify that the signal for the sensor is stable at different set points between the low idle position and 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 to determine if all of the injector solenoids are being energized by the ECM.
Perform the "Cylinder Cutout Test" on Cat® ET to identify any misfiring cylinders. Refer to Troubleshooting, "Injector Solenoid Circuit - Test" for more 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. Refer to Testing and Adjusting, "Air in Fuel - Test" for more information.
Cold weather adversely affects the characteristics of the fuel. Refer to Operation and Maintenance Manual for information on improving the characteristics of the fuel during 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" 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
Check for an air filter restriction. Clean plugged air filters or replace plugged air filters. Refer to the Operation and Maintenance Manual.
Check the air inlet and exhaust system for restrictions and/or leaks. Refer to Systems Operation/Testing and Adjusting, "Air Inlet and Exhaust System". Incorrect Torque Convertor Speed Output Sensor Signal (D8T, D9T, and D10T Tier 3 Models Only)
A torque convertor speed output sensor that is out of adjustment can cause rapid engine speed change that creates an engine misfire sound.
Use Cat® ET datalogger to view "Desired Engine Speed (RPM)" and "Torque Convertor Speed (RPM)". Set the data log for a sample rate of .25 seconds intervals and operate the engine. Look for an erratic signal that will cause torque convertor overspeed protection to spike, resulting in rapid engine speed changes. Note: Refer to Special Instruction, "Using the Caterpillar Electronic Technician (ET) Data Log" for instructions on configuring a data log in Cat® ET.
If an erratic torque convertor speed output signal is seen, readjust or replace the sensor. Refer to Testing and Adjusting, "Speed Sensor - Adjust - Output Speed of the Torque Converter".
Illustration 1 g03731721
Cat® ET data log view of an erratic TC speed signal that caused an "engine misfire" symptom