Fuel supply on a tuned pump

OM617 Fuel Lift Pumps

For a tuned diesel injection pump equipped with larger elements—such as 7.5mm, 7.7mm, or 8mm plungers—intended for a Mercedes OM617 turbo engine, an electric lift pump or a heavy-duty mechanical lift pump is the best choice to keep up with the increased fuel demand.

The original, standard mechanical lift pump found on the OM617 engine block simply cannot provide sufficient volume and pressure at high RPMs to adequately supply a tuned injection pump.

The second photo provides a clear overview of the pro and cons of each type to help you make your choice. 

Why an Electric Pump Is Often the Best Choice

When an OM617 injection pump is modified for higher power output, the larger plungers require a constant supply pressure (typically between 1 and 1.5 bar / 15–22 PSI, depending on the pump builder) to prevent cavitation—the formation of air bubbles—within the pump.

Constant Pressure: An electric pump delivers the correct pressure the moment you turn the ignition key. This also facilitates easier cold starts and simplifies the bleeding process.

Popular Models: Many tuners opt for the Carter P4600HP or Holley Blue pumps (such as the 12-803BP or 12-802-1). These are designed for diesel applications, offer high flow rates, and are built to withstand engine vibrations.

Important: Always use an external fuel pressure regulator with a return line to the fuel tank. This prevents the pressure from becoming too high, which could otherwise damage the internal seals of the injection pump. Don't forget to replace the banjo bolt with a built-in pressure valve—located at the rear of the pump—with a standard banjo bolt. After all, your fuel pressure regulator now handles the fuel pressure, not this pressure-regulating bolt.

Installation advice

If you opt for an electric fuel pump, keep the following points in mind:

Position the pump as close to the fuel tank as possible and mount it low (electric pumps are more efficient at pushing fuel than pulling it).

Install a coarse pre-filter before the electric pump to prevent debris from the tank from damaging the pump.

Always connect the pump via a relay that is triggered by the ignition switch.

For a tuned OM617 injection pump, you should ideally aim for a constant supply pressure of approximately 1.0 to 1.4 bar (15–20 PSI) under full load.

The alternative: Mechanical Pump

If you prefer the legendary reliability of a purely mechanical system (without any electronics), you cannot continue using the original pump.

Modified mechanical pump

A pump from an OM601/602/603 engine can be fitted to a tuned setup and provides a higher flow rate than the original OM615/616/617 pump.

Drawback: The output remains dependent on engine speed. At idle or at extremely high RPMs, the pressure may fluctuate compared to an electric version.

Another disadvantage of these pumps is that you cannot prime the fuel system by hand, as you can with the original OM615/616/617 pump. Consequently, you have to crank the engine for a long time to get the diesel into the pump and bleed the system, which places a heavy load on both the starter motor and the battery.

This explanation is based on my own personal experience, as well as insights shared by other tuners. I accept no responsibility for the accuracy of this information. If you have any comments or other suggestions, please email me at info@dietro.be