2008 Mercedes-Benz ML320 Diesel Injection Pump Replacement Cost

After the fuel injection pump fails, the fuel distributor and injectors will not have sufficient power to drive the vehicle without severe driveability issues. Also, continuing to drive with a failed high pressure fuel pump could lead to metal shavings being passed through the fuel system as the fuel pump continues to spin. Since modern diesel fuel systems have return fuel lines, the metal shavings can make their way through the high pressure fuel pump, through the fuel distributor, to the injectors, and through the return line to the fuel tank, and back into the new LPFP, once replaced. To help avoid this costly repair, the vehicle should be towed to a repair facility.

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.

The injector pump may be replaced when the problem is actually dirty fuel filter(s), low engine compression, worn out glow plugs, failed fuel supply pump, defective glow plug relay, improper injector pump timing, and/or poor fuel quality.

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

The injection pump may fail if the fuel supply pump doesn't deliver the proper amount of fuel to the injection pump. Therefore, it's very important that the supply pump is checked and replaced if necessary.