3176C, 3406E and 3456 Industrial Engines Troubleshooting – Engine Top Speed Is Not Obtained

Note: If this fault occurs only under load, refer to Troubleshooting, “Acceleration Is Poor or Throttle Response Is Poor”.

Probable Causes


  • Diagnostic codes 
  • Event codes 
  • Derates 
  • Cold mode 
  • Engine parameters 
  • Throttle signal 
  • “Turbocharger outlet (boost) pressure sensor” 
  • Atmospheric pressure sensor 
  • Air inlet and exhaust system 
  • Fuel supply 
  • Cylinder performance 
  • Accessory equipment 

Recommended 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. A status screen on Cat ET will display a derate if a derate is active.

Cold Mode

Connect Cat ET to the service tool connector. Verify that the engine has exited cold mode.

Engine Parameters

Verify that the correct engine parameters are being used.

Throttle Signal

Connect Cat ET to the service tool connector. View the status for the throttle position on the status screen. Operate the throttle from the low idle position to the high idle position. The status should be 0 percent at low idle and the status should be 100 percent at high idle. If the status can not operate in the full range, refer to Troubleshooting, “Speed Control – Test”.

“Turbocharger Outlet (Boost) Pressure Sensor” and Atmospheric Pressure Sensor


  1. Monitor the status of “Fuel Position”, of “Rated Fuel Limit”, and of “FRC Fuel Limit” on Cat ET while the engine is operating under full load. These parameters must reflect the information below.
    Table 1
    “Fuel Position” = “Rated Fuel Limit”
    “Fuel Position” < “FRC Fuel Limit”

    If “Fuel Position” equals “Rated Fuel Limit” and “Fuel Position” is less than “FRC Fuel Limit”, the electronics are operating correctly. Otherwise, proceed with the next Step.


  1. Monitor the status of “Turbocharger Outlet (Boost) Pressure” and “Atmospheric Pressure” for normal operation on Cat ET. When the engine is not running, “Turbocharger Outlet (Boost) Pressure” should be 0 kPa (0 psi).

Air Inlet and Exhaust System


  1. Check the air filter restriction indicator, if equipped. Clean plugged air filters or replace plugged air filters. Refer to the Operation and Maintenance Manual.


  1. Check the air inlet and exhaust system for restrictions and/or leaks. Refer to Systems Operation/Testing and Adjusting.

Fuel Supply


  1. 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.


  1. Ensure that the fuel supply valve (if equipped) is in the full OPEN position.


  1. 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.


Do not crank the engine continuously for more than 30 seconds. Allow the starting motor to cool for two minutes before cranking the engine again.


  1. 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 injectors 

    Note: A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel. Refer to Systems Operation/Testing and Adjusting.


  1. Check the fuel tank for foreign objects which may block the fuel supply.


  1. Check the fuel filters.


  1. Check the diesel fuel for contamination. Refer to Systems Operation/Testing and Adjusting.


  1. 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


  1. Check the valve lash and reset the valve lash, if necessary. Refer to Systems Operation/Testing and Adjusting for the procedure.


  1. Check for correct installation of the unit injector connectors. Check for correct installation of all other applicable connectors. Refer to Troubleshooting, “Electrical Connectors – Inspect”.


  1. Perform the “Injector Solenoid Test” on Cat ET in order to determine if all of the injector solenoids are being energized by the ECM.


  1. Perform the “Cylinder Cutout Test” on Cat ET in order to identify any injectors that might be misfiring.


  1. If Cat ET indicates a problem, remove the electronic unit injector from the suspect cylinder. Refer to Disassembly and Assembly.


  1. 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 


  1. Perform all necessary repairs. Ensure that the repairs have eliminated the problem.


  1. If the repair does not eliminate the problem, reinstall the electronic unit injectors that were removed and continue with this test procedure.

Accessory Equipment

Check all accessory equipment for problems that may create excessive load on the engine. Repair any damaged components or replace any damaged components.

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