MBE 4000 DDEC VI Troubleshooting – Section 11.4 Defective Fuel Pump

Section 11.4
Defective Fuel Pump

To determine if the fuel pump is causing excessive white smoke, perform the following to check fuel intake pressure upstream of fuel pump. Refer to "3.5 Test #4 Upstream Pressure Test" .‪

1. If the pressure at idle speed (600-650 rpm) is in the normal range of -0.09 to -0.12 bar (-1.3 to -1.7 psi [-9 to -12 kPa]), check for aerated fuel. Refer to "11.5 Aerated Fuel" .
2. If the pressure at idle speed (600-650 rpm) is greater than -0.09 to -0.12 bar (-1.3 to -1.7 psi [-9 to -12 kPa]); listed in Table "Problem — The Fuel Inlet Pressure is Too High" .
3. If the pressure at idle speed (600-650 rpm) is less than -0.09 to -0.12 bar (-1.3 to -1.7 psi [-9 to -12 kPa]); listed in Table "" .
4. If a no pressure reading is observed, replace the fuel pump, refer to "11.4.1 Replace Faulty Fuel Pump" .

   Problem — The Fuel Inlet Pressure is Too High ‪
   Possible Cause ‪	Remedy ‪
   The fuel feed lines are kinked or blocked.‪	Inspect the lines and fittings for blockage. Repair/replace as necessary.‪
   The suction line and/or strainer at the fuel level sensor is blocked or is touching the bottom of the fuel tank.‪	Inspect the suction line and/or strainer through the fuel fill opening in the fuel tank. Remove the fuel level sensor and repair or replace the line or strainer, as necessary.‪
   The check valve in the fuel feed line is blocked or not open wide (the flange at the fitting connection is bent).‪	Repair/replace as necessary.‪

   Table 1. Problem — The Fuel Inlet Pressure is Too High

   Problem — The Fuel Inlet Pressure is Too Low ‪
   Possible Cause ‪	Remedy ‪
   The pre-filter is leaking (drawing air).‪	Replace the O-ring. Replace the filter element and tighten the cap on the filter housing 25 N·m (18 lb·ft).‪
   The fuel feed lines and connections are leaking (drawing air).‪	Replace the seals on the leaking lines. Tighten the fittings on the fuel lines to 25 N·m (18 lb·ft) and perform a fuel leak test.‪
   The fuel pump is worn.‪	Replace the fuel pump.‪
   The pressure limiting valve in the fuel pump is jammed open or the drive lever is loose or broken.‪	Replace the fuel pump.‪
   The air-admission valve in the fuel tank is blocked.‪	Remove air-admission valve blockage.‪
   The suction line and/or strainer at the fuel level sensor is blocked or is touching the bottom of the fuel tank.‪	Inspect the suction line and/or strainer through the fuel fill opening in the fuel tank. Remove the fuel level sensor and repair or replace the line or strainer, as necessary‪

Section 11.4.1
Replace Faulty Fuel Pump

Perform the following steps for the replacement of the fuel pump:‪

1. Replace the fuel pump, refer to MBE 4000 Service Manual (6SE420), Chapter 2, “Fuel System — Fuel Pump”.
2. Test the engine to determine if the white smoke problem was resolved; refer to "11.4.1.1 Engine Test with Replaced Fuel Pump" .

Section 11.4.1.1
Engine Test with Replaced Fuel Pump

To determine if the replaced fuel pump resolved excessive white smoke difficulty, perform the following steps:‪

PERSONAL INJURY ‪
To avoid injury before starting and running the engine, ensure the vehicle is parked on a level surface, parking brake is set, and the wheels are blocked.‪

1. Start and run the engine, if no white smoke is visible, no further troubleshooting is required. Shut down the engine.
2. If white smoke is visible, check for aerated fuel; refer to "11.5 Aerated Fuel"