Fuel pump filter

Fuel pump and filter is mounted on the left frame floor in front of the rear axle.

M3 - Fuel pump 55/1 - Fuel filter with integrated fuel pressure regulator approx. 3.8 bars

Fuel Pump

Illustration shows screw spindle pump M3 - Fuel pump

The task of the pump is to supply an adequate quantity of fuel to the fuel system at the required pressure in all driving states.

On model W220 helical spindle pump is mounted at frame floor.

Illustration shows screw spindle pump 1 - Rotating spindle 2 - Drive spindle 3 - Check valve 4 - Pressure relief valve 5 - Electric motor 6 - Ground connection 7 - Voltage supply a - Fuel from the fuel tank b - Fuel to the fuel filter

The fuel pump (M3) pumps more fuel than the engine requires in total in order to maintain the pressure in the fuel system in all operating states. As a result of this circulation, relatively cool fuel is available at all times for injection (avoids the formation of vapor bubbles). A pressure relief valve (4) is integrated in the fuel pump in order to limit the pressure.

The check valve (3) in the fuel pump decouples the fuel system from the fuel tank by preventing fuel from flowing back through the fuel pump to the fuel tank. The fuel pump is actuated by the engine control unit through the fuel pump relay.

Parts

• A0014701294 (EUR 370)
• BOSCH 0986580354 (EUR 173)
• PIEBURG 7.28126.51.0 (EUR 155)
• TOPRAN 401632 (EUR 95)
• STARKE 162-029 (EUR 30)

Filter

The task of the fuel filter is to filter impurities out of the fuel, maintaining constant fuel pressure in wide limits irrespective of the fuel pump delivery.

55/1 - Fuel filter with integrated fuel pressure regulator CAN - Pressurization line PUMP - Feed from fuel pump TANK - Return flow to fuel tank MOT - To engine

55/1 - Fuel filter with integrated fuel pressure regulator 55/3 - Valve 55/5 - Diaphragm (membrane) 55/6 - Compression (push) spring 55/9 - Filter element insert 55/40 - Diaphragm pressure regulator A - Feed from fuel pump b - Diaphragm pressure regulator vent line B - Fuel return flow to fuel tank C - Fuel pressure connection to engine

The fuel filter consists of a sheet metal casing with an integrated filter element (55/9). The fuel flows through this from the outside to the inside. As a result any impurities are trapped.

The diaphragm pressure regulator (55/40) controls the fuel pressure of approx. 3.8 bar (operating pessure) via the fuel return flow quantity to the fuel tank.

If the set fuel pressure is exceeded, the diaphragm (55/5) is pushed against the push spring (55/6) and the valve (55/3) attached to the diaphragm opens the passage for the fuel return to the fuel tank (B). If the set pressure is below the limit, the valve is closed again by means of the push spring.

Fuel pressure as a function of the fuel pump delivery

A - Fuel pressure in bar B - Fuel pump delivery in liters per hour

A greatly varying fuel pump delivery (e.g. 20 or 140 l/h) does not have any great effect on the fuel pressure.