No Power To Fuel Pump

[WayneW124]

New to the world of Mercedes Benz, I recently acquired a 1991 W124 w/m103 for the low price of $200. Car is in very good condition, it was thought to have a blown head gasket, but the initial inspection showed no signs of blown head gasket, upon further inspection I discovered the water pump was bad, replaced wp and the car drove like a dream. the more I drove the car, the more I realized why people love this model of Mercedes. As well as the car drove I couldn't get it to pass emissions, so I turn to a local shop that specialize in German car repairs. I had discovered a couple of vacuum leaks that I pointed out to the shop, the shop tech didn't concern himself with the vacuum leaks, but instead leaned the air and fuel mix. this made the car hard to start but it passed emissions, after 2 days of the car being hard to start, I discovered the radiator had gone bad and I replaced it, now that everything is put back together, I have no power to the fuel pumps, I hooked the test light directly to the pumps to check current to them and nothing. I replaced fuel pump relay and the MAS Module along with checking the over voltage protection relay and still no power to fuel pump. can anyone point me in the right direction so I can continue to enjoy this superb automobile.

[Usaguy]

because your car is a 1991 model it doesn't have a fuel pump relay it's done by the MAS relay.

Make sure that your MAS relay is fully seated in the plug. You have to turn the knob on the top clockwise when you install it.


You should have battery voltage (12V) at terminal #1 on the MAS plug (unfused)

#2 terminal on this plug goes to the fuel pumps

test this stuff.


wiring diagrams on page 31 and page 5 apply to your car:

http://www.w124-zone.com/downloads/MB%20CD/W124/w124CD1/Program/ETM/ETM.pdf

[WayneW124]

Christuna, thank you for the input, I re-checked the MAS relay and it is seated properly with the dial turned all the way to the lock position. I want to make sure I'm testing the terminals properly, with the MAS relay out, I'm looking for 12volts at port/terminal 1, is this direct current from the battery and terminal #2 is what carry that 12 volts to the fuel pump? I was unable to get to the link with the diagram, but I will keep trying.

[Usaguy]

yes #1 is direct from the battery unfused and #2 goes to the fuel pumps the link works so you may want to try a different browser (it's like 270 pages)