C9.3 Marine Auxiliary and Generator Set Engine Caterpillar

Engine Misfires, Runs Rough or Is Unstable

Usage:

C9.3 C93

Note: Refer to Troubleshooting, "Cat ET Service Features" for information about service features.

Probable Causes

Active codes and logged codes
Low quality fuel
Fuel injectors
Lack of lubrication
Valve train components
Gear train and components of the lower end

Recommended Actions

Note: The procedures have been listed in order of probability. Complete the procedures in order.

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Table 1
Troubleshooting Test Steps	Values	Results
1. Active Codes and Logged Codes A. Establish communication between Caterpillar^® Electronic Technician (Cat ET) and the Electronic Control Module (ECM). Refer to Troubleshooting, "Electronic Service Tools", if necessary. B. Download the "Warranty Report" from the engine ECM before performing any troubleshooting or clearing diagnostic trouble codes. Troubleshoot any active codes before continuing with this procedure.	Codes	Result: There are no active codes. Proceed to Test Step 2. Result: There are active codes. Repair: Troubleshoot any active codes before continuing with this procedure. If the problem is not resolved, proceed to Test Step 2.
2. Fuel Quality A. Refer to Operation and Maintenance Manual for information on the proper characteristics of the fuel for the engine. If necessary, obtain a fuel analysis in order to confirm that the correct fuel is being used for the engine. Refer to Systems Operation/Testing and Adjusting, "Fuel Quality - Test" for the proper procedure.	Fuel	Result: The fuel quality is OK. Proceed to Test Step 3. Result: The fuel quality is not OK. Repair: Replace the fuel. Verify that the repair eliminated the problem. If the problem is not resolved, proceed to Test Step 3.
3. Fuel Injectors A. Use Cat ET to ensure that there are not any active diagnostic codes for the injector solenoids. Perform the "Cylinder Cutout Test" in order to check for a misfiring cylinder. Refer to Troubleshooting, "Injector Solenoid - Test" for information that is related to the test. Use Cat ET to perform the "Fuel System Verification Test" in order to check the mechanical condition of the fuel injectors. Refer to Troubleshooting, "Injector Solenoid - Test" for information that is related to the test.	Injector Solenoid Test or Fuel System Verification Test	Result: The test was successful. Proceed to Test Step 4. Result: The test was not successful. Repair: Diagnose the problem and then repair the problem. Reset all active codes and clear all logged codes. Verify that the repair eliminated the problem. If the problem is not resolved, proceed to Test Step 4.
4. 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. Clean any oil passages that are questionable. Refer to the Disassembly and Assembly 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: Make the necessary repairs, Verify that the repair eliminated the problem. If the problem is not resolved, proceed to Test Step 5.
5. Valve Train Components A. Check the valve lash. Refer to Troubleshooting, "Valve Lash Is Excessive". B. Check for damage to valve train components. Remove the valve cover from the suspect cylinders. Check the following items for damage: 1. Camshaft 2. Valve rotocoil 3. Valve springs 4. Camshaft followers 5. Rocker shaft 6. Bridges 7. Pushrods 8. Injectors Refer to the Disassembly and Assembly for additional information. C. Check for valves that do not move freely. Remove the cylinder head and inspect the valves. Refer to the Disassembly and Assembly 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: Make the necessary repairs, Verify that the repair eliminated the problem. If the problem is not resolved, proceed to Test Step 6.
6. Gear Train and Components of the Lower End A. Inspect the gear train and lower end components.	Gear Train	Result: The gear train or lower end components are damaged. Repair: Replace any damaged parts. 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).