Fuel Supply System E53

4. Fuel Supply System E53

4.4. Fuel supply system E53:

4.1 Description of parts
1. Fuel tank (plastic)
2. Electric fuel delivery pump
3. Pressure relief valve
4. Non-return flap
5. Filler neck
6. Tank expansion line
7. Suction jet pump
8. Overflow protection valve
9. Fuel filler cap
10. Fuel feed line
11. Fuel return line
12. Refuelling vent line
13. Operating vent line
14. Pressure check line (USA only)
15. Expansion tank
16. Flood valve
17. Rollover valve
18. Pressure regulator
19. Fuel filter
20. Fuel rail
21. Fuel evaporation control valve
22. Engine control unit
23. Intake manifold
24. Flush line
25. Activated carbon filter
26. Breather pipe
27. Tank leak diagnosis module
28. Dust filter


4.2 Functional description (See to drawing 4.4)

Fuel system
The saddle-shaped fuel tank is equipped with an electric fuel delivery pump in the smaller, right-hand side.

The suction jet pump in the left-hand side of the fuel tank transfers fuel via the tank expansion line to the right-hand side of the fuel tank.

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.

The flood valve on the underside of the expansion tank protects the system against overfilling when refuelling. The rising fuel level in the refuelling vent line closes the flood valve and so creates an overpressure in the fuel tank, which prevents the tank from being filled any further.

Fuel supply to the engine



Ventilation System USA
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 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 lines.

The condensed components of the fuel vapours are fed back from the expansion tank into the fuel tank through the vent lines.

The rollover valve on the top of the expansion tank will close in the event of the vehicle turning over. This prevents fuel from draining out 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 with a supply of fresh air through the tank leak diagnosis module and the 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
See ventilation system USA with the following differences:
1. The activated carbon filter has a smaller capacity.
2. The tank leak diagnosis module and dust filter (See drawing 4.4, view A) are eliminated.
3. The pressure check line is eliminated.


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.

4.3 Fuel system operating data
Pressure regulator: 3.5 bar
Operating pressure of suction jet pump: 1 - 1.3 bar.