Fuel Pump
 

Ok, while troubleshooting my no start problem on my '99 E300D I have come across a fuel pump relay(in K40 Relay) and a fuel pump fuse in the battery fuse box. What are these for? I thought the car only had a mechanical lift pump?

Since no one has responded; as far as I know you only have the Mechanical Fuel Supply/Lift Pump.

It is likely the Relay and or Fuse is being used for something else and you will need a Wiring Diagram to find out for sure.

Same elecrical box as used in a gas car perhaps? Almost would have to be as there is no provision for any form of electric fuel pump on the diesels. If the car runs with the relay or whatever removed you would be sure it is at least not there for a fuel supply function.

Parts of the relay may be used for some other fuel system funtion though is a possibility. Like a complex fuel level reader. Doubtful mercededs would have installed it for no function at all. Costs money and would be pointless to do so.

The K40 relay supplies power to the SOV as well as numerous other componenets. If I rememeber correctly, one of the fuses on top of it protects the SOV and possibly GP relay. If the SOV doesn't open, no fuel moves.

The fuel pump is a mechanical suction pump mounted on the side of the IP aft of the SOV. There isn't an electrical pump anywhere.