807504A 1 Mercruiser CARBURETOR ASSEMBLY

Probable Causes
Active engine derate
Cold Mode
Throttle switch
Turbocharger outlet pressure sensor
Atmospheric pressure sensor
Fuel supply
Air inlet and exhaust system
Accessory equipmentRecommended Actions
Active Engine Derate
Use ET to check for logged engine derates and/or active engine derates. A status flag will appear on ET if a derate is active. The engine speed might be limited due to one of the following conditions: high altitude, dirty air filters and other factors.Cold Mode
Use ET to verify that the engine has exited Cold Mode. A status flag will appear if the engine is operating in Cold Mode. This may limit engine speed.Throttle Signal
Monitor the throttle switch on ET. Verify that the switch is operating. Refer to Troubleshooting, "Throttle Switch Circuit - Test" for the proper troubleshooting procedure.Turbocharger Outlet Pressure Sensor or Atmospheric Pressure Sensor
Monitor the status of "Fuel Position", "Rated Fuel Limit", and "FRC Fuel Limit" on ET while the engine is operating under full load. These parameters should reflect the information below.
Table 1
"Fuel Position" = "Rated Fuel Limit"    
AND    
"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.
Monitor the status of "Boost Pressure" and "Atmospheric Pressure" for normal operation on ET. When the engine is not running, "Boost Pressure" should be 0 kPa (0 psi).Fuel Supply
Check the fuel lines for the following problems: restrictions, collapsed lines and pinched lines. If problems are found with the fuel lines, repair the lines and/or replace the lines.
Check the fuel tank for foreign objects which may block the fuel supply.
Check for air in the low pressure 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
Replacement of unit injectorsNote: A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel. Refer to Testing and Adjusting for more information.
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.
Purge air from the low pressure fuel supply circuit. Refer to Operation and Maintenance Manual, "Fuel System - Prime" for the correct procedure.
Check fuel quality. In temperatures below 0 °C (32 °F), check for solidified fuel (wax). Refer to Special Instruction, SEBD0717, "Diesel Fuels And Your Engine".
Check the fuel pressure during engine cranking. Check the fuel pressure after the fuel filter. Refer to Testing and Adjusting for the correct pressure values. If the fuel pressure is low, replace the fuel filters. If the fuel pressure is still low, check the following items: fuel transfer pump, fuel transfer pump coupling and fuel pressure regulating valve.Air Inlet and Exhaust System
Observe the check engine lamp. Check for an air filter restriction indicator. 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 Testing and Adjusting, "Air Inlet and Exhaust System".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.