16 00 Fuel supply system E46 (diesel engines)

General function description for fuel systems.

The saddle-shaped fuel tank contains the surge chamber with the electric fuel feed supply pump on its right side.

The surge chamber ensures that the fuel supply pump is properly supplied in all vehicle operating states.

The fuel is repumped from the right side of the fuel tank into the surge chamber via the suction jet pump integrated in the tank expansion line. The suction jet pump is operated via the fuel feed line.

The outlet protection valve protects the fuel return line. The valve closes in the event of a pressure drop when the fuel return line is damaged or disconnected.

This prevents fuel from escaping from the fuel tank in extreme vehicle positions (overturning, inclined position).

Fuel supply to engine:

M47 (see Fig 1)

The fuel is routed from the electric fuel supply pump via the fuel feed line and the fuel filter to the distributor injection pump.

The distributor injection pump supplies the relevant injection nozzle.

The return fuel from the fuel injectors and the distributor injection pump is directed to the bimetallic valve, which divides the amount of return fuel as a function of the fuel temperature.

At low fuel temperatures, the greater part of the fuel flows back into the fuel feed line ahead of the fuel filter. In this way, the fuel is heated up faster at low outside temperatures.

At high fuel temperatures, the greater part of the fuel flows back into the fuel tank via the fuel cooler and the fuel return line. This prevents the fuel from being excessively heated at high outside temperatures.

Large and heated amounts of return fuel occur under extreme operating conditions such as e.g. uphill driving or trailer towing. For this reason, part of the fuel is routed directly into the fuel feed line by the flow restrictor in the H-piece. This measure also counteracts any excessive heating of fuel in the fuel tank.

M57 (see Fig 2)

The fuel is routed from the electric fuel supply pump via the fuel feed line, the inline pump and the fuel filter to the high-pressure pump.

The high-pressure pump supplies the injection nozzles with fuel via the fuel rail.

The inline pump generates the necessary preliminary fuel pressure for the high-pressure pump. This preliminary pressure is maintained at a constant level by the pressure limiting valve in the engine circuit.

The return fuel from the fuel injectors and the high-pressure pump is directed to the bimetallic valve, which divides the amount of return fuel as a function of the fuel temperature.

At low fuel temperatures, the greater part of the fuel flows directly into the fuel feed ahead of the inline pump. In this way, the fuel

At high fuel temperatures, the greater part of the fuel flows back into the fuel tank via the fuel cooler and the fuel return line. This prevents the fuel from being excessively heated at high outside temperatures.

Large and heated amounts of return fuel occur under extreme operating conditions such as e.g. uphill driving or trailer towing. For this reason, part of the fuel is routed directly into the fuel feed line by the flow restrictor in the H-piece. This measure also counteracts any excessive heating of fuel in the fuel tank.

Venting system (see Fig 1 and Fig 2 )

The fuel tank is vented during refueling via the refueling vent line in the filler necks.

During driving, the fuel tank is vented via the service vent lines and the expansion tank.

The condensed constituents of the fuel vapors pass from the expansion tank via the left service vent line back into the fuel tank.

Determining fill level in fuel tank

The fuel level is measured by means of lever-type sensors on both sides of the fuel tank. The right lever-type sensor is integrated in the fuel supply unit. The left lever-type sensor is located in the left sensor unit. The combination of the determined ohm values from the right and left lever-type sensors produces the actual level in the fuel tank.

Working pressure of fuel supply pump: 0.4 bar

Working pressure of suction jet pump: 1 - 1.3 bar

Fig 1: Schematic Drawings Of Fuel Supply Systems (Fuel Supply System E46 M47)

Courtesy of BMW OF NORTH AMERICA, INC.

1. 5.1 Fuel supply system E46 M47
   Fig 2: Schematic Drawings Of Fuel Supply Systems (Fuel Supply System E46 M57)

   Courtesy of BMW OF NORTH AMERICA, INC.
2. 5.2 Fuel supply system E46 M57