aerobat

Hey guys! I've search high and low with no luck, so I'm hoping you can help me. I recently had to replace my fuel pump in my early '01 C320. I ran into the typical issue with incompatible wiring harnesses, but that was an easy fix since all of the connectors on the pump and fuel sending unit were the same. The pump works perfectly and the car runs great. My issue came when I realized the fuel sending unit wasn't working correctly. It turns out, they changed the resistance range on the sending unit in in the 06/01 and on models. I can't find any of the early '01 fuel pumps anymore and they only make the later model pumps. I'm kicking myself for throwing away the old pump after replacement. My question is: Does anyone know the spec resistance range for the early '01 fuel sending unit on the right side (fuel pump)?

aerobat

VDO and Mercedes were absolutely no help here. So I hooked up a potentiometer to the wiring harness and measured full at around 0 ohms and empty at close to 210 ohms. Since the units are wired in series and the left hand unit measured at 105 ohms at empty, the right hand unit is the same and also measures up to 105 ohms. Replacement fuel pumps for the later model cars go from 50-680 ohms, so a 130ohm resistor wired in parallel will allow you to use the new model pumps with the old model cars. I did this myself yesterday and it works perfectly! I'm just passing this along if anyone else finds themselves in a similar situation.

samaritrey

Thanks for updating us this should be helpful for many in the future.

giftcp

The resistor in parallel solves the top resistance. However the equivalent resistance in parallel of the 50ohms and 130ohms does not come down to near zero. As such the tank would never be full even if you top it up. I guess