MERCEDES BENZ Axor Service Manual

MBE 4000 SERVICE MANUAL

2.9 FUEL SYSTEM INSPECTION

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

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.

To avoid injury from fire, keep all potential ignition sources away from diesel fuel, open f lames, sparks, and electrical resistance heatingelements. Do not smoke whenrefueling.

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 2-2.

Component Torque

Transfer Tube Nut 45 N·m (33 lb·ft)

High Pressure Line Nuts 30 N·m (22 lb·ft)

Table 2-2 Torque Specifications for Fuel Line Nuts

5. Perform a fuel pressure test. Refer to section 2.9.1.

All information subject to change without notice.

2.9 FUEL SYSTEM INSPECTION

2.9.1 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 2-23. Setup 2 has the gauge installed before the fuel filter. See Figure 2-24.

1. Fitting 4. Fuel Outlet Line

2. Fuel Filter Housing 5. Unit Pump

3. Mechanical Gauge

Figure 2-23 Gauge Installation – After the Fuel Filter

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MBE 4000 SERVICE MANUAL

1. Fuel Pump 4. Fuel Outlet Line

2. Fitting 5. Mechanical Gauge

3. Fuel Filter Housing

Figure 2-24 Gauge Installation–BeforetheFuelFilter 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.

All information subject to change without notice.

2.9 FUEL SYSTEM INSPECTION

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.

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 th e outside. Do not modify or tamper with the exhaust system or emission control system.

2. Start the engine and warm i t up to working temperatures: 80 -95C (176 - 203 F).

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 2-3. 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 5.5–6.5bar(80–95psi)

Maximum difference between fuel filter housing

inlet and outlet pressure

0.3 bar (4 psi)

Table 2-3 Fuel System Specifications for Pressure

2.9.1.1 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 PLD-MR heat exchange plate.

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MBE 4000 SERVICE MANUAL

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.

2.9.2 Performing a Fuel System Test using minidiag2

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

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

-203 F).

(176

1. Plug your minidiag2 into the truck diagnostic connector and follow the instructions in the

minidiag2 Supplement Manual to connect to the VCU/PLD-MR system.

2. After establishing the connection with the truck, choose option 4 – Routines.

3. UnderRoutinessection,selectoption4–IdleSmoothlyBalance.

-95 C

All information subject to change without notice.

2.9 FUEL SYSTEM INSPECTION

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 2.9.2.1.

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.

2.9.2.1 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:

or Highest Positive:

1. Check torque at all the transfer tubes nuts (45 N·m [33 lb·ft]). 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, c heck 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.

or Lowest Negative:

1. Check torque at all the transfer tubes nuts (45 N·m [33 lb·ft]). 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 t est). The readings must be 75% or higher. For readings lower than 75%, remove the oil pan and cylinder head and check for damaged components.

All information subject to change without notice.

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