Probable Causes
- Poor fuel quality
- Air in fuel
- Low fuel pressure
- Restriction in the fuel return line
- Fuel leakage from fuel injection line
- Faulty fuel injection nozzle
- Incorrect fuel setting
- Faulty fuel injection pump
- Incorrect fuel injection timing
- Faulty automatic timing advance unit
- Incorrect valve setting
- Air inlet restriction
- Internal engine problem
Recommended Repairs
Poor Fuel Quality
Ensure that there is good, clean fuel in the tank. When possible, interview the operator in order to determine if fuel quality is in question. Try to determine if the engine started misfiring soon after refueling. Refer to Troubleshooting, "Fuel Quality".
Air in the Fuel
Check for air in the fuel system. Refer to Troubleshooting, "Air In Fuel".
Low Fuel Pressure
Replace the primary fuel filter and the secondary fuel filter. Check the fuel lines for blockage or damage. If this is not the cause, check the fuel transfer pump. Repair the fuel transfer pump or install a new fuel transfer pump. Refer to Systems Operation, Testing and Adjusting, "3406C Diesel Truck Engine".
Restriction in the Fuel Return Line
The fuel return line is connected to a constant bleed orifice that is part of the elbow. Check the constant bleed orifice for blockage. The fuel return line should have a constant flow of fuel when the engine is running.
Fuel Leakage From Fuel Injection Line
Check the fuel injection lines for leakage. If the fuel injection line nuts are loose, tighten to 40 ± 7 N·m (30 ± 5 lb ft).
Faulty Fuel Injector Nozzle
The fuel injection nozzles are not serviced. Remove the injectors from the engine and refer to System Operation, Testing and Adjusting, "3406C Diesel Truck Engine" for the proper testing procedure. Replace the fuel injector nozzles, as needed.
Incorrect Fuel Setting
The fuel setting procedure can be performed with the governor and fuel injection pump on the engine. Refer to System Operation, Testing and Adjusting, "3406C Diesel Truck Engine" for the correct procedure.
Faulty Fuel Injection Pump
Test the fuel injection pump. Refer to the Tool Operating Manual, "Install and Test Fuel Injection Pumps Used on 3406B, 3406C, and 3406 PEEC Engines Using the 4C8192 Heavy-Duty Coupling on Fuel Injection Equipment Test Stand" for the test procedure.
Incorrect Fuel Injection Timing
Check Fuel Injection Timing. Refer to Systems Operation, Testing And Adjusting, "3406C Diesel Truck Engine" for details.
Faulty Automatic Timing Advance Unit
Check the operation of the automatic timing advance unit. Refer to Systems Operation, Testing And Adjusting, "3406C Diesel Truck Engine".
Incorrect Valve Setting
Check valve adjustment. Refer to Systems Operation, Testing And Adjusting, "3406C Diesel Truck Engine".
Air Inlet Restriction
Check the air flow with a water manometer or a vacuum gauge. Connect the gauge to the engine air inlet between the air cleaner and the inlet to the turbocharger. Check the air flow with the engine at full load rpm. The maximum allowable air inlet restriction is 6.25 kPa (25 inches of H2O). If the indication is higher than the maximum permissible restriction, clean the filter element or install a new filter element. Check the restriction again. If the restriction remains too high, inspect the air inlet piping for obstructions.
Internal Engine Problem
Check for signs of damaged valves, damaged cylinder head gasket, etc.