3512B Marine Auxiliary Engine Caterpillar

Note: If this problem occurs under load, refer to the diagnostic procedure Troubleshooting, "Low Power/Poor Or No Response To Throttle".

The probable root causes are listed in order below:

• Personality Module

• Low Idle/High Idle Switch

• Fuel supply

• Air inlet or exhaust restriction

• Leaks in air system

• Faulty accessory equipment

Perform the following test in order:

1. Verify that the correct Personality Module is installed. Refer to the diagnostic procedure Troubleshooting, "Programming Parameters".

2. Use the Caterpillar Electronic Technician (ET) in order to monitor the status of the Low Idle/High Idle switch. Observe the switch position. Move the switch from the Low Idle position to the High Idle position. The Cat ET should indicate the correct position. Perform the diagnostic functional test Troubleshooting, "Low Idle/High Idle Switch".

3. Check fuel lines for the following problems: restrictions, collapse and pinched line. Repair the lines and/or replace the lines. Refer to Systems Operation, "Fuel System".

   1. Check the fuel tank for foreign objects which may block the fuel supply. Check for air in the low pressure fuel supply system after you perform the following procedures:
      • Replacing the fuel filters

      • Working on the low pressure fuel supply circuit

      • Replacing fuel injectors

   2. Purge air from the low pressure fuel supply circuit with the hand priming pump and by cranking the engine in 30 second cycles. After you crank the engine, stop for two minutes. This will allow the starting motor to cool. Loosen the vent plug on the fuel return. The plug is located on the rear upper left side of the engine block. Hand prime the engine again if air in fuel continues. A sight glass in the low pressure supply line is helpful in diagnosing air in the fuel.

   3. Check fuel quality. In temperatures below 0 °C (32 °F), check for solidified fuel (wax). Check the fuel pressure while the engine is cranking. Check the fuel pressure at the filter. Refer to the Specifications manual for correct pressure values. If the pressure is low, check for plugged 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. Check for a combustion problem.

4. Check air inlet and exhaust systems for restrictions and/or leaks. Refer to the Systems Operation.

5. Observe the Check Engine Lamp. Check for a air filter restriction indicator. Replace plugged air filters and/or clean filters. Refer to the Testing and Adjusting, "Air Inlet and Exhaust System". Perform the diagnostic functional test Troubleshooting, "Engine Sensor Open/Short Test".

6. Check all accessory equipment.