C175 Tier 4 Final Engines for Off-Highway Trucks Caterpillar

Engine Misfires, Runs Rough or Is Unstable

Usage:

793F D3T

Use this procedure to troubleshoot an engine that misfires, runs rough, or is unstable.

Note: If the problem is intermittent and the problem cannot be duplicated, refer to Troubleshooting, "Power Is Intermittently Low or Power Cutout Is Intermittent".

Note: If the problem only occurs under certain conditions, test the engine under those conditions. Examples of certain conditions are high rpm, full load, and engine operating temperature. Troubleshooting the symptoms under other conditions can give misleading results.

Probable Causes

Fuel system
Fuel Injectors
Parameters
Lubrication
Valve train components
Gear train

Recommended Actions

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Table 1
Troubleshooting Test Steps	Values	Results
1. Inspect the Fuel System Refer to Testing and Adjusting, "Fuel System Inspection" for additional information. A. Visually check the fuel level in the fuel tank. Do not rely on the fuel gauge only. B. Ensure that the vent in the fuel cap is not filled with debris. C. Ensure that the fuel supply valve (if equipped) is in the full OPEN position. Note: Cold weather adversely affects the characteristics of the fuel. Refer to the engines Operation and Maintenance Manual for information on improving the characteristics of the fuel during cold-weather operation. D. Check fuel quality. Refer to Testing and Adjusting, "Fuel Quality - Test" for additional information. Check the fuel tank for debris or foreign objects which may block the fuel supply. E. Check for fuel leaks.	Fuel System	Result: The fuel system is OK. Proceed to Test Step 2. Result: The fuel system is NOT OK. Repair: Repair or replace damaged fuel system components. If the problem is not resolved, proceed to Test Step 2.
2. Test the Fuel Injectors A. Connect Cat^® Electronic Technician (ET) to the service tool connector. B. Use Cat ET to perform the following fuel injector tests: - "Injector Solenoid Test" - "Cylinder Cutout Test" Refer to Troubleshooting, "Cat ET Service Features" for additional information.	Fuel Injectors	Result: The tests were successful. Proceed to Test Step 3. Result: The tests were not successful. Repair: Release the pressure in the high-pressure rail by loosening the end plug on one of the last 2 fuel accumulators. Refer to Testing and Adjusting, "Fuel Rail Pressure - Release" for instructions on how to release the pressurized fuel. Verify the "Fuel Rail Pressure" reading in ET is 0 ± 8 MPa (1160 psi) prior to servicing the fuel system. Remove the injector and accumulator/quill tube from the suspect cylinder to inspect. If damaged, replace as necessary. If the injector and accumulator/quill tube are not damaged, continue to inspect the cylinder for other damage. Repair or replace the failed components. If the problem is not resolved, proceed to Test Step 3.
3. Check for Incorrect Configuration Parameters A. Connect Cat ET. B. Use Cat ET to verify that the correct parameters are being used.	Parameters	Result: The parameters are correct. Proceed to Test Step 4. Result: The parameters are not correct. Repair: Input the correct parameters. Refer to Troubleshooting, "Configuration Parameters" for additional information. If the problem is not resolved, proceed to Test Step 4.
4. Check for Proper Lubrication A. Check for proper lubrication of the valve components. Check for sufficient lubrication between the injector tappets and the rocker arms. B. Check for blocked oil passages. Oil passages must be clean. Refer to the Disassembly and Assembly manual for additional information. C. Inspect the engine oil filters for ferrous material. D. Obtain an S·O·S oil analysis. The analysis will contribute to a better understanding of oil contamination and the origin of the contamination.	Lubrication	Result: The oil passages are not blocked and the engine has proper lubrication. Proceed to Test Step 5. Result: The oil passages are blocked or the engine does not have proper lubrication. Repair: Clean oil passages. Repair or replace damaged components. If the problem is not resolved, proceed to Test Step 5.
5. Inspect the Valve Train Components A. Remove the valve mechanism cover and the camshaft covers. B. Check the valve lash. Refer to Testing and Adjusting, "Valve Lash - Adjust". C. Check the following valve train components for damage: - Camshafts - Valve rotocoils - Valve springs - Camshaft followers - Rocker shafts - Bridges D. Check for valves that do not move freely. Remove the cylinder head and inspect the valves. Refer to the Disassembly and Assembly manual for additional information.	Valve Train	Result: The valve train components are not damaged. Proceed to Test Step 6. Result: The valve train components are damaged. Repair: Repair or replace damaged valve train components. If the problem is not resolved, proceed to Test Step 6.
6. Inspect the Gear Train A. Check the following gear train for damage: - Crankshaft gear - Camshaft drive gear B. Verify that the crankshaft and the camshaft drive gears are set with the proper orientation for engine timing. Refer to Testing and Adjusting, Camshaft Timing and Crankshaft Position for Valve Lash Setting.	Gear Train	Result: The gear train has excessive wear. Repair: Repair or replace damaged gear train components. Refer to the Disassembly and Assembly manual and the Reuse and Salvage Guidelines manual for additional information. Verify that the repair eliminated the problem.

If the procedure did not correct the issue, contact your Cat dealer Technical Communicator (TC). For further assistance, your TC can confer with the Dealer Solutions Network (DSN).