C18 Marine Auxiliary and Marine Generator Set Engines Caterpillar

Engine Misfires, Runs Rough or Is Unstable

Usage:

C18 DTP

The probable root causes are listed in order below:

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

Diagnostic codes
Electrical connectors
Fuel quality
Electronic unit injectors
Air intake and exhaust system
Cold mode operation
Throttle
Valve lash

Recommended Actions

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Table 1
Troubleshooting Test Steps	Expected Results	Results
1. Diagnostic Codes A. Check for active diagnostic codes on Caterpillar Electronic Technician (ET). Troubleshoot any active codes before continuing with this procedure.	Codes	Result: There are active codes. Troubleshoot any active codes before continuing with this procedure. Result: There are no active codes. Proceed to Test Step 2.
2. Inspect the Electrical Connectors and the Wiring A. Stop the engine. Remove electrical power from the Electronic Control Module (ECM). B. Proceed to Troubleshooting, "Electrical Connectors - Inspect"	Electrical connectors and wiring	Result: Harness and connectors appear to be OK. Proceed to Test Step 3. Result: There is a problem with the connectors and/or wiring. Perform the necessary repairs to the connectors and/or wiring.
3. Check the Fuel Quality A. Obtain a fuel analysis in order to confirm that the fuel quality is OK for this engine.	Fuel quality	Result: The fuel quality is OK. Proceed to Test Step 3. Result: The fuel quality in not OK. Replace the fuel. Verify that the repair eliminated the problem. If the problem is not resolved, proceed to the next step.
4. Electronic Unit Injectors A. Perform the "Injector Solenoid Test" on Cat ET in order to determine if all of the injector solenoids are being energized by the ECM. B. Perform the "Cylinder Cutout Test" on Cat ET in order to identify any injectors that might be misfiring. There may be a problem with the throttle. Refer to Troubleshooting, "Speed Control - Test".	Fuel injectors	Result: The electronic unit injectors are operating properly. There is no electrical problems or misfiring cylinders. Proceed to Test Step 4. Result: The test was not successful. Diagnose the problem and then repair the problem. Reset all active codes and clear all logged codes. Verify that the repair eliminated the problem.
5. Air Intake and Exhaust System A. Check the air filter restriction indicator, if equipped. Clean plugged air filters or replace plugged air filters. Refer to the Operation and Maintenance Manual. B. Check the air inlet and exhaust system for restrictions and/or leaks. Refer to Systems Operation/Testing and Adjusting. C. Check the performance of the turbocharger. Ensure that the recommended maintenance is performed on the turbocharger.	Air inlet system and exhaust system	Result: The air filter, air inlet system, exhaust system, and turbocharger are operating properly. Proceed to Test Step 6. Result: The air filter is restricted, air inlet and/or exhaust system is restricted and leaking, or problem with the turbocharger is found. Repair or replace any necessary components. If the problem is not resolved, proceed to the next step.
6. Cold Mode Operation A. Cold mode is activated whenever the engine coolant temperature falls below a predetermined value. Monitor the status screen on Cat ET in order to verify that the engine has exited cold mode. Observe the reading for coolant temperature on the Cat ET.	Cold mode	Result: The engine is operating in cold mode. This is normal operation. Return the engine to service. Result: The engine is not operating in cold mode. If the problem is not resolved, proceed to the next step.
7. Throttle A. There may be a problem with the throttle. Refer to Troubleshooting, "Speed Control - Test"	Throttle	Result: The throttle is operating correctly. Proceed to Test Step 8. Result: The throttle is not operating correctly. Make the necessary repairs. Verify that the problem is resolved.
8. Check the Valve Lash Adjustment for the Engine A. Check the valve lash settings for each cylinder. Refer to Systems Operation/ Testing and Adjusting.	Valve lash	Result: The valve lash setting is not correct for one or more cylinders. As necessary, set the valve lash for the cylinders.