3412 Generator Set Caterpillar

Engine Misfires, Runs Rough or Is Unstable

Usage:

3412 DK6

Probable Causes

Engine derate or active codes
Electrical connectors
Low compression (cylinder pressure)
Individual malfunctioning cylinder
Valve lash
Faulty fuel injector nozzle
Throttle signal
Fuel supply
Air inlet and exhaust system

Recommended Actions

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Table 1
Troubleshooting Test Steps	Value	Results
1. Check for Engine Derate or Active Codes. A. Some engine monitoring parameters that trigger an engine derate do not produce an event code. Connect Cat^® Electronic Technician (ET) in order to check for a derate of the engine. B. Certain diagnostic codes may cause poor performance. Use Cat ET to check for active codes and for logged codes.	Engine derate Diagnostic codes	Result : The engine derate and/or diagnostic codes are OK. Proceed to Test Step 2. Result : The engine derate and/or diagnostic codes are NOT OK. Repair : Troubleshoot any active diagnostic codes that are present. If the problem is not resolved, proceed to Test Step 2.
2. Check the Electrical Connectors. A. Check for correct installation of the J1/P1 ECM connector.	Electrical connectors	Result : The electrical connectors are OK. Proceed to Test Step 3. Result : The electrical connectors are NOT OK. Repair : Refer to Troubleshooting, "Electrical Connectors - Inspect". If the problem is not resolved, proceed to Test Step 3.
3. Check for Low Compression Cylinder Pressure. A. Perform a compression test. Refer to Systems Operation, Testing and Adjusting, "Compression - Test ". B. If low compression is noted on any cylinders, investigate the cause and rectify the cause. Possible causes of low compression are shown in the following list: - Faulty piston -Faulty piston rings - Worn cylinder bores - Worn valves - Faulty cylinder head gasket - Damaged cylinder head	Low compression	Result : The cylinder pressure is OK. Proceed to Test Step 4. Result : The cylinder pressure is NOT OK. Repair : Perform all necessary repairs. If the problem is not resolved, proceed to Test Step 4.
4. Check for Individual Malfunctioning Cylinders. A. With the engine speed at a fast idle, loosen the high-pressure fuel line to the fuel injector of number one cylinder. If there is any reduction in engine speed, tighten the high-pressure fuel line to the fuel injector. B. Individually repeat this procedure for each fuel injector.	Cylinders	Result : The cylinders are OK. Proceed to Test Step 5. Result : The cylinders are NOT OK. Repair : Repair the malfunctioning cylinder as necessary. If the problem is not resolved, proceed to Test Step 5.
5. Check the Valve Lash. A. Check valve lash on misfiring cylinder.	Valve lash	Result : The valve lash is OK. Proceed to Test Step 6. Result : The valve lash is NOT OK. Repair : Refer to Testing and Adjusting, "Engine Valve Lash - Inspect/Adjust" for the correct procedure. If the problem is not resolved, proceed to Test Step 6.
6. Check for a Faulty Fuel Injector Nozzle. A. Remove the suspect fuel injection nozzle. B. Test the nozzle by using the 5P-4150 Nozzle Testing Group. Refer to Systems Operation, Testing and Adjusting, "Fuel System" for the proper testing procedure.	Fuel injector nozzle	Result : The fuel injector nozzles are OK. Proceed to Test Step 7. Result : The fuel injector nozzles are NOT OK. Repair : Replace the fuel injector nozzles, as needed. If the problem is not resolved, proceed to Test Step 7.
7. Check the Throttle Signal. A. 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.	Throttle signal	Result : The throttle signal is OK. Proceed to Test Step 8. Result : The throttle signal is NOT OK. Repair : If a problem is suspected with the throttle, refer to the appropriate troubleshooting procedure for troubleshooting the throttle signal. If the problem is not resolved, proceed to Test Step 8.
8. Check the Fuel Supply. A. Visually check the fuel level. Do not rely on the fuel gauge only. B. Check the fuel lines for the following problems : restrictions, collapsed lines, and pinched lines. C. Check the fuel tank for foreign objects which may block the fuel supply. D. Prime the 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 Note : 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.	Fuel supply	Result : The fuel supply is OK. Proceed to Test Step 9. Result : The fuel supply is NOT OK. Repair : If necessary, add fuel. If the engine has been run out of fuel, it will be necessary to prime the fuel system. Refer to Operation and Maintenance Manual for the correct procedure. If problems are found with the fuel lines, repair the lines and/or replace the lines. Remove any foreign debris found in the fuel tank. If the problem is not resolved, proceed to Test Step 9.
9. Check the Air Inlet and Exhaust System for Leaks and/or Restrictions. A. Check the air filter restriction indicator for a plugged filter. B. Check the air inlet and exhaust system for restrictions and/or leaks.	Air inlet and Exhaust system	Result : The air inlet system is NOT OK. Repair : If necessary, service the engine. Refer to the Operation and Maintenance Manual. Result : The exhaust system is NOT OK. Repair : Refer to Systems Operation/Testing and Adjusting.

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