Skip to main content

MBE 4000 FUEL SYSTEM INSPECTION

Perform the following steps to inspect the fuel system for damage: ‪

PERSONAL INJURY

To avoid injury from penetrating fluids, do not put your hands in front of fluid under pressure. Fluids under pressure can penetrate skin and clothing.

FIRE

To avoid injury from fire, keep all potential ignition sources away from diesel fuel, including open flames, sparks, and electrical resistance heating elements. Do not smoke when refueling.

Note: For additional safety precautions, refer to the General Information section of the MBE 4000 Service Manual (6SE412).

  1. Check fuel delivery lines looking for deformation or bent lines, creating restriction and/or obstruction of the flow.
  2. Check suction lines and connections looking for damage or under torque, allowing air to enter the fuel system.
  3. Check the fuel tank installation. Look for bent/blocked lines, and leaks.
  4. Check high-pressure lines for leaks. Look for connector nut leaks at the unit pump and at the transfer tube on the cylinder head. In the event of leaks, disassemble and inspect the high-pressure lines/transfer tube. For proper torque specifications, see those listed in Table .

    Component ‪

    Torque ‪

    Transfer Tube Nut ‪

    45 Nm (33 lbft) ‪

    High Pressure Line Nuts ‪

    30 Nm (22 lbft) ‪

    Torque Specifications for Fuel Line Nuts
  5. Perform a fuel pressure test. Refer to section .

Performing a Fuel Pressure Test

Perform the following steps to conduct a fuel pressure test: ‪

  1. Install the pressure gauge on the fuel system. There are two possible setups for this installation. Setup 1 has the gauge installed after the fuel filter. See Figure 43558 . Setup 2 has the gauge installed before the fuel filter. See Figure 43559 .

    1. Fitting ‪

    4. Fuel Outlet Line ‪

    2. Fuel Filter Housing ‪

    5. Unit Pump ‪

    3. Mechanical Gauge ‪

    Gauge Installation After the Fuel Filter

    1. Fuel Pump ‪

    4. Fuel Outlet Line ‪

    2. Fitting ‪

    5. Mechanical Gauge ‪

    3. Fuel Filter Housing ‪

    Gauge Installation Before the Fuel Filter

    Note: The fitting applied in both setups is not a special tool and it is not included in the Mercedes-Benz kit or SPX kit. This fitting is a component and it can be ordered from Canton PDC under part number 915039012205.

    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.

    PERSONAL INJURY

    Diesel engine exhaust and some of its constituents are known to the State of California to cause cancer, birth defects, and other reproductive harm.

    • Always start and operate an engine in a well ventilated area.
    • If operating an engine in an enclosed area, vent the exhaust to the outside.
    • Do not modify or tamper with the exhaust system or emission control system.
  2. Start the engine and warm it up to working temperatures: 80- 95C (176 - 203F).
  3. Check the fuel pressure at two points: idle speed and rated speed.
  4. Compare the test results with the fuel systems specifications for pressure listed in Table . If any of the readings are out of spec, follow the proper troubleshooting steps.

    Speed ‪

    Pressure ‪

    Fuel Pressure Test at idle rpm ‪

    2 bar (29 psi) minimum ‪

    Fuel Pressure Test at rated rpm ‪

    5.5 6.5 bar (80 95 psi) ‪

    Maximum difference between fuel filter housing inlet and outlet pressure ‪

    0.3 bar (4 psi) ‪

    Fuel System Specifications for Pressure
Fuel Pressure Test Troubleshooting Procedures

For results out of specs on the fuel pressure test, check the following appropriate steps: ‪

  1. At idle rpm, with fuel pressure lower than 2 bar (29 psi), check the following:
    • Check the pressure valve at the end of the fuel gallery. Look for opening pressure 2 bar (29 psi).
    • Check the fuel pump assembly (bearing and/or driven gear).
    • Check to see if the fuel system is drawing air.
  2. At rated rpm, for fuel pressure lower than 5.5 bar (80 psi), check the following:
    • Check the water separator filter condition.
    • Check for restriction at the check valve on the DDEC-ECU heat exchange plate.
    • Check the main fuel filter condition, looking for saturation or any damaged seal allowing flow of fuel from the pressure side to the return side.
    • Check for leaks at the suction lines from the tank.
    • Check the fuel pump assembly (bearing and/or driven gear).
    • Look for leaks and/or a damaged fuel pump.
    • Check for restriction at the check valve on the fuel filter return line to tank.
  3. At rated rpm, for fuel pressure higher than 6.5 bar (95 psi), check the following:
    • Check the return line and injector spill line, looking for restrictions or bent lines.
    • Check the fuel pressure valve for a blocked or restricted regulator orifice.

Performing a Fuel System Test using minidiag2

To perform a fuel system test using minidiag2, perform the following steps: ‪

PERSONAL INJURY

To avoid injury when working near or on an operating engine, remove loose items of clothing and jewelry. Tie back or contain long hair that could be caught in any moving part causing injury.

PERSONAL INJURY

Diesel engine exhaust and some of its constituents are known to the State of California to cause cancer, birth defects, and other reproductive harm.

  • Always start and operate an engine in a well ventilated area.
  • If operating an engine in an enclosed area, vent the exhaust to the outside.
  • Do not modify or tamper with the exhaust system or emission control system.

Note: Before running the test, warm the engine to normal operating temperatures: 80-95C (176-203F).

  1. Plug your minidiag2 into the truck diagnostic connector and follow the instructions in the minidiag2 Supplement Manual to connect to the VCU/DDEC-ECU system.
  2. After establishing the connection with the truck, choose option 4 Routines.
  3. Under Routines section, select option 4 Idle Smoothly Balance.
  4. Check each cylinder value for this routine and compare your results with the troubleshooting and proceed as described for any results out of spec. Refer to section .
  5. Still connected to truck, look for option 5 Impact Time Delay, under the Routines section.
  6. Select it and check each cylinder value for this routine and compare your results with the troubleshooting and proceed as described for results out of spec.
Idle Smoothly Balance Troubleshooting

This test measures the percentage of fuel delivery for each cylinder in order to maintain a smooth operation at idle. Operational range for this test: from -3% (negative)to 3% (positive). ‪

Identify the cylinder with the biggest absolute value highest positive or lowest negative. The troubleshooting steps for both conditions are: ‪

For Highest Positive:

  1. Check torque at all the transfer tubes nuts (45 Nm [33 lbft]). Run the test again. If the results are out of operational range, proceed to next step.
  2. Find the cylinder with the result closest to zero. Swap the injector nozzle holder and the transfer tube between this cylinder and the cylinder with the highest result. Run the test again. If the highest result follows the injector nozzle holder, replace the nozzle holder. If not, proceed to the next step.

    Note: After removing the injector nozzle holders and transfer tubes, check the coupling area between both components and the seal rings. If any defect or damage is found, replace the damaged parts.

  3. Return both injector nozzle holders and transfer tubes to their original positions and run the impact delay time and compression test routines.

For Lowest Negative:

  1. Check torque at all the transfer tubes nuts (45 Nm [33 lbft]). Run the test again. If the results are out of the operational range, proceed to the next step.
  2. Find the cylinder with the lowest result, remove the injector nozzle holder and check the opening pressure. If the pressure is lower than the minimum spec (275 bar [3989 psi]), replace the injector nozzle holder. If the pressure is within the spec, proceed to the next step.
  3. Run a compression test using minidiag2, ProLink reader, or DDDL 5.0 (refer to the Diagnostic Tool Manual for instructions to run this test). The readings must be 75% or higher. For readings lower than 75%, remove the oil pan and cylinder head and check for damaged components.
Impact Delay Time Troubleshooting

This test measures the reaction time of the unit pumps. The operation range is from 1.2 to 2.1 milliseconds. Perform the following troubleshooting procedure for values out of the operating range: ‪

  1. Check the engine harness from the DDEC-ECU to the suspected unit pump connectors and wire. Look for bad or loose connections and broken wires. If there are none, proceed to the next step.
  2. Swap the suspect unit pump with one operating properly and run the test again. Refer to section for unit pump removal and refer to section for unit pump installation. If the condition follows the unit pump, replace the unit pump.
Checking the Fuel Pump Driven Gear Bolt Torque

This procedure describes how to check the fuel pump driven gear bolt torque. Insufficient torque on the bolt will impact engine performance. ‪

  1. Remove the fuel pump.
  2. Set a clicker-type torque wrench to 30 Nm (22 lbft).

    NOTICE:

    Do not apply a torque over 30 Nm (22 lbft). Excessive torque can cause the bolt/gear failure. ‪

  3. Turn the torque wrench as shown by the arrow in until the torque wrench clicks. This resistance ensures that the fuel pump drive gear bolt is in good condition. In the event of NO resistance found with shaft turning freely, proceed to step 4. See Figure 45119 .

    1. Torque Wrench ‪

    3. Fuel Pump ‪

    2. Fuel Pump Drive Gear Splines ‪

    4. Fuel Pump Gasket ‪

    Checking Fuel Pump DriveGear

  4. Remove the camshaft gear cover. See Figure 45120 .
  5. Remove the bolt and use a puller to remove the gear. See Figure 45120 .

    1. Camshaft Gear Cover ‪

    4. Fuel Pump Drive Gear ‪

    2. Drive Gear Mounting Bolt ‪

    5. Camshaft Gear Cover Gasket ‪

    3. Fuel Pump Drive Bearing Shaft ‪

    Removing/Installing Fuel Pump Drive Gear and Bolt

  6. Check the mounting between bolt, gear, and shaft. Look for damaged parts. Replace damaged parts.
  7. Install gear and bolt. Apply Loctite 271 sealant to the bolt threads and install gear and bolt. Install the fuel pump gear locking device (J 46187) to the fuel pump drive splines and secure the shaft from turning while torquing bolt. See Figure 45119 .
  8. Torque bolt to 35 Nm (26 lbft).
  9. Install the camshaft cover and the gasket. Torque to 50 Nm (37 lbft).
  10. Install the fuel pump and a new fuel pump gasket. Torque the fuel pump bolts to 25 Nm (18 lbft).