Mercedes-Benz ML250 Diesel Injection Pump Replacement Cost

High pressure fuel pumps on diesel engines have incredibly long service lives. They tend to last between 100,000 and 150,000 miles, and repeat replacements are not typical. A small handful of European commuter cars recommend replacement as scheduled maintenance, but this is a very small number. It is important that the fuel pump be periodically inspected for leaks, wear, shaft play, and metal shavings, as failure of the injection pump can send these metal shavings through the entire fuel system.

When the injection pump fails, diagnostics will lead the technician to the fuel system quickly. Not only will the technician find a sizeable drop in fuel rail pressure, but the fuel system may be completely full of metal shavings. When these shavings are spotted, the technician will likely remove and inspect the high pressure fuel pump, where the metal shavings originated. The technician will go about examining and removing fuel system components subjected to these shavings, replacing those components which must operate at extreme pressures, and salvaging low pressure items where possible.

Replacing the injection pump normally involves removal of an engine mount, for transverse or small-engine diesels, removal of all accessory components, the timing cover, timing components, high and low pressure fuel lines, and finally, the pump and associated electrical connectors may be removed. Reassembly is the reverse of removal, and if the pump failed, the system will be thoroughly inspected before allowing the vehicle to restart. Full step-by-step procedures for the two common types of diesel injection pumps can be found below: Gear Driven Injection Pump

1. Disconnect the negative battery terminal
2. Remove any components that obstruct access to the injection pump
3. Disconnect all fuel lines and electrical connectors to the injector pump
4. Remove the injector drive gear cover, if equipped
5. Lock the injector drive gear in place with the locking pin
6. Remove the fasteners that secure the injector pump
7. Remove the old injector pump and clean the mounting area
8. Install the new injector pump and "time it" with the drive gear
9. Secure the new injector pump with its fasteners
10. Reconnect all electrical connectors and fuel lines
11. Install any other removed components
12. Reconnect the negative battery terminal and clear any codes
13. Start the engine and verify the injector timing with the proper tool
14. Perform a comprehensive test drive to verify the repair

Timing Belt Driven Injection Pump

1. Disconnect the negative battery terminal
2. Remove any drive belts that block access to the injection pump
3. Disconnect any fuel lines and electrical connectors
4. Remove the timing belt cover(s) and, by hand, rotate the engine to the timing marks
5. Loosen the timing belt and pull it back from the injection pump
6. Remove the injection pump fasteners and the injection pump
7. Clean the mounting area and install the new injection pump
8. Secure the injection pump fasteners and re-attach the timing belt
9. Verify that the alignment of the timing marks are still correct
10. Install the timing cover, drive belts, fuel lines, and electrical connectors
11. Reconnect the negative battery terminal and clear any codes
12. Perform a comprehensive test drive to verify the repair

We recommend repairing this vehicle outside, and draining the fuel tank before removal. These two safety steps will prevent injury to the DIYer or the professional. Lastly, there is a risk of fire, vapor leaks, and inhalation injury when the fuel tank has been opened. We recommend using the OEM sealant when reinstalling the fuel pump. If you smell fumes inside the vehicle after the repair, consult the repair facility immediately.

Unlike gasoline fuel systems, the components of a diesel system are manufactured to much higher standards, and are under much more stringent conditions. This greatly influences the cost of repair to diesel delivery systems, and should emphasize the need to properly maintain the diesel fuel delivery system according to factory recommendations. Lastly, on-board diagnostic (OBD) scanners may function in most vehicles, but not in select American trucks. The scanner should be universal, but some vehicles simply alert that there is no connection. For these situations, there may be an issue with the OBDII port or the scanner, or there may be a compatibility issue between the two.

Replacing high pressure diesel injection parts is dangerous, and methods for mitigating risk must be thoroughly understood and followed. Also, diagnosis of a faulty injection pump can be very difficult for a DIYer. This task is easier for a professional because they have the luxury of years of formal training, field experience, excellent scanning equipment, and have performed this repair previously in most cases. We recommend trusting a professional technician with the diagnosis and repair of faulty high pressure diesel fuel delivery system components. .