2.2 Functional Description

(Please refer to Figure - Figure).

Fuel System 

The right-hand side of the saddle-shaped fuel tank has a surge chamber with the electric fuel delivery pump.

The surge chamber guarantees correct fuel supply from the fuel delivery pump in all operating states of the vehicle.

Fuel is transferred from the right-hand side of the fuel tank to the surge chamber by the suction jet pump integrated in the tank expansion line. The suction jet pump is driven by the fuel return line.

The pressure relief valve controls the pressure required for the suction jet pump to operate. The overflow protection valve protects the fuel return line. Should the pressure drop in the event of damage or the fuel return line becoming separated, the valve will close.

This prevents the fuel from overflowing from the fuel tank in extreme vehicle positions (rollover, inclination).

The non-return flap prevents the fuel from sloshing back in the fuel filler neck when the fuel pump nozzle cuts off.

Fuel Supply To The Engine 

M43TU/52TU  (Please refer to Figure, view A)

For description of "Fuel supply system E38/39, 1.2 Functional description, fuel supply system for engine M52TU", please refer to Figure - Figure.

M52 USA and M73 (please refer to Figure and Figure).

For description of "Fuel supply system E38/39, 1.2 Functional description, fuel supply system for engine M52 USA and M73", please refer to Figure - Figure.

M54 (please refer to Figure, view B and drawing 1.7/1.8Figure and Figure).

For description of "Fuel supply system E38/39, 1.2 Functional description, fuel supply system for engine M54/62TU", please refer to Figure - Figure.

Ventilation System USA  (Please refer to Figure and Figure).

When refuelling, the fuel tank is ventilated through the refuelling vent line.

Due to its large cross-sectional area, the refuelling vent line quickly feeds the displayed volume (fuel vapours) via the expansion tank to the activated carbon filter.

The activated carbon absorbs the fuel contained in the fuel vapours. The purified air is then fed into the atmosphere through the breather pipe, the leak diagnosis pump or the tank leak diagnosis module and dust filter.

Ventilation during operation of the vehicle is maintained in the same manner through the refuelling vent line and operating vent line.

The condensed components of the fuel vapours are fed back from the expansion tank into the fuel tank through the left-hand operating vent line.

In the event of overfilling, the float valve in the expansion tank will be closed by the rising fuel level. This prevents the expansion tank from filling.

The rollover valve on the top of the expansion tank will close in the event of the vehicle turning over. This prevents the fuel from escaping into the activated carbon filter.

The activated carbon filter is regenerated by flushing out with fresh air.

The engine control unit opens the fuel evaporation control valve. This applies the vacuum generated in the engine intake manifold to the flush line.

In this way, the activated carbon filter is flushed out. The required fresh air is fed through the leak diagnosis pump or the tank leak diagnosis module and dust filter. The components of fuel gathered by the activated carbon filter are fed into the engine's combustion through the air supply and the flush line.

This process is only possible with the engine running.

Ventilation System- All Countries  (please refer to Figure).

Please refer to ventilation system USA with the following differences:

1. When refuelling, the fuel tank is ventilated through the refuelling vent line, which feeds the displaced volume into the fuel filler neck. Instead of the refuelling vent line (USA) with a large cross-sectional area, there is a second operating vent line with a smaller cross-sectional area. The float valve is eliminated.
2. The activated carbon filter has a smaller capacity.
3. The leak diagnosis pump or tank leak diagnosis module and dust filter are eliminated.
4. For Japan vehicles, an auxiliary vent line with a float valve in the expansion tank is installed in place of the refuelling vent line (USA). This is connected to the refuelling vent line (all countries).

   This modification is necessary due to the higher level of gas emissions of the fuel available in Japan (please refer to Figure).

Leak Detection For Tank Ventilation System USA  (lease refer to Figure and Figure).

For description of "Fuel supply system E38/39, 1.2 Functional description, leak detection for tank ventilation system USA", please refer to Figure - Figure.

Fuel Level Measurement In The Fuel Tank 

The fuel level is measured by a lever-type sensor on each side of the fuel tank. The right-hand lever-type sensor is integrated into the fuel delivery unit. The left-hand lever-type sensor is located in the left-hand sensor unit. The actual fuel level in the tank is determined by linking the ohm values of the left and right-hand lever-type sensors.