MBE 900 DDEC VI Troubleshooting – Section 5.10 Fuel Pump

Section 5.10
Fuel Pump

To determine if the fuel pump is causing starting difficulty, perform the following:‪

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 fuel pump suction at idle speed (600–650 rpm) is -0.09 to -0.12 bar (-1.3 to -1.7), check for aerated fuel. Refer to "5.11 Aerated Fuel" .
2. If fuel pump suction at idle speed (600–650 rpm) is less than -0.09 to -0.12 bar (-1.3 to -1.7), refer to Table "Problem — The Fuel Inlet Suction is Too Low" .

   Problem — The Fuel Inlet Suction 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.‪

   Table 2. Problem — The Fuel Inlet Suction is Too Low
3. If the suction at idle speed (600–650 rpm) is greater than -0.09 to -0.12 bar (-1.3 to -1.7), refer to Table "Problem — The Fuel Inlet Suction is Too High" .

   Problem — The Fuel Inlet Suction 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 3. Problem — The Fuel Inlet Suction is Too High
4. If a no reading is observed, replace the fuel pump, refer to MBE 900 Service Manual (6SE9007), fuel system chapter.

Section 5.10.1
Fuel Pump Replacement

Perform the following steps for fuel pump replacement:‪

1. Replace the fuel pump, refer to MBE 900 Service Manual (6SE9007), fuel system chapter:

   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.‪

2. Test the engine to determine if starting has been improved; refer to "5.10.1.1 Engine Test with Replaced Fuel Pump" .

Section 5.10.1.1
Engine Test with Replaced Fuel Pump

To determine if the replaced fuel pump resolved starting 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. Attempt to start and run the engine, if the engine starts and runs, no further troubleshooting is required. Shut down the engine.
2. If the engine fails to start and run, check for aerated fuel; refer to "5.11 Aerated Fuel" .