Mercedes-Benz W126 fuel pump not delivering: checklist
Why does the W126 not start when the tank is almost empty?
The fuel pump does not suck by itself but needs fuel pushed to the supply side under pressure. From an almost empty tank not enough comes. The car usually starts only after you refuel generously, about twenty litres.
Why does the W126 stall while driving even though there is plenty of fuel in the tank?
The pre-filter inside the tank, the strainer, can clog. When the level drops, fuel no longer flows through the strainer to the pump. The strainer is replaced from under the car through the service hatch at the bottom of the tank. A clogged strainer can also be in the fuel distributor's inlet pipe or in the connector of the pipe going to the injection.
The pump does not run, what should be checked?
First check the pump fuse: it is one of the 8 A fuses labelled on the cover (Fuel pump or Kraftstoffpumpe). Next the relay. The pump is above the rear axle together with the fuel filter. Replacing the relay alone is not always enough: the fault can be in the pump itself or in the distributor cap and rotor.