881579 Mercruiser NUT

Probable Causes
Diagnostic codes
Event codes
Derates
Engine parameters
Throttle signal
Air inlet and exhaust system
Fuel supply
Cylinder performanceRecommended Actions
Diagnostic Codes, Event Codes and Derates
Certain diagnostic codes, event codes and/or derates may cause poor performance. Connect Caterpillar Electronic Technician (ET) and check for active codes and/or for logged codes. Troubleshoot any codes that are present before continuing with this procedure.If this application supports engine derates, use Cat ET to check for logged derates. Refer to Troubleshooting, "Event Code List" for the specific events that are applicable to this application. A status screen on Cat ET will display a derate if a derate is active.Engine Parameters
Verify that the correct engine parameters are being used.Throttle Signal
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.Air Inlet and Exhaust System
Check the air filter restriction indicator, if equipped. 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.Fuel Supply
Visually check the fuel level. Do not rely on the fuel gauge only. If necessary, add fuel. If the engine has been run out of fuel, it will be necessary to purge the air from the fuel system. Refer to Operation and Maintenance Manual.
Ensure that the fuel supply valve (if equipped) is in the full OPEN position.
Check the fuel lines for the following problems: restrictions, collapsed lines, pinched lines and loose connections. If problems are found with the fuel lines, repair the lines and/or replace the lines.
Prime the fuel 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 injectorsNote: A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel. Refer to Systems Operation/Testing and Adjusting.
Check the fuel tank for foreign objects which may block the fuel supply.
Check the fuel filters.
Check the diesel fuel for contamination. Refer to Systems Operation/Testing and Adjusting.
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.Cylinder Performance
Check the valve lash and reset the valve lash, if necessary. Refer to Systems Operation/Testing and Adjusting for the procedure.
Check for correct installation of the unit injector connectors. Check for correct installation of all other applicable connectors. Refer to Troubleshooting, "Electrical Connectors - Inspect".
Perform the "Injector Solenoid Test" on Cat ET in order to determine if all of the injector solenoids are being energized by the ECM.
Perform the "Cylinder Cutout Test" on Cat ET in order to identify any injectors that might be misfiring.
If Cat ET indicates a problem, remove the electronic unit injector from the suspect cylinder. Refer to Disassembly and Assembly.
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
Perform all necessary repairs. Ensure that the repairs have eliminated the problem.