Fuel Management

Fuel Management
Fuel Tank





The fuel tank is made of high density polyethylene (reduced weight) layers which is manufactured to meet safety requirements.
The fuel tank has a capacity of 70 litres (18.5 gad, including a reserve capacity of 10 litres.
A midchassis mounted saddle type tank (1) is used providing a tunnel for the driveshaft but creates two separate lower chambers.
The E60 fuel tank design reduces the potential evaporative emissions. This design reduces the number of external connections and openings by increasing the amount of "in tank" or integral components including molding the filler pipe to the tank.
The fuel tank is held in place by 2 retaining bands. The tank is secured in the middle by a plastic lug formed into the tank. All body contact points are insulated with foam or rubber.





The service access caps are located at the top of the fuel tank. The following components can be accessed from the vehicle interior:
^ Right swirl pot, fuel pump, fuel level sensor, suction jet pump, fuel lines to left tank half and left suction jet pump.
^ Left fuel level sensor, fuel filter and fuel pressure regulator.
The six pin wiring harness connector is located on the right service cap. The six pin wiring harness connector has 2 wires for the fuel pump power supply and 2 wires for both fuel level sensors. The fuel feed line is connected to the left service cap with a quick release coupling.

Fuel Delivery Unit





The fuel delivery unit located in the fuel tank ensures bubble free fuel delivery under all operating conditions. In case of service, the left and right fuel delivery units can be removed completely. The two fuel level sensors can be replaced individually.

Swirl Pot
The swirl pot contains the electric fuel pump and a suction jet pump and is open at the top. The base of the swirl pot features an outlet protection valve, which allows fuel to flow from the right tank half into the swirl pot. It prevents the fuel from flowing back into the right tank half (trap).
The swirl pot ensures that the fuel pump is always immersed in fuel so that the pump does not draw in air. Bubble free fuel delivery is very important particularly at low fuel levels and under high driving dynamics conditions when the tank is almost completely empty.





Fuel System





Fuel Delivery

Fuel Row: Right tank half => swirl pot => fuel pump => fuel filter => fuel rail.
The fuel is pumped into the right tank half. The swirl pot contains the electric fuel pump. Fuel passes through the valve incorporated in the base of the swirl pot into the swirl pot. When the fuel level is higher, fuel also enters the swirl pot from the top.
The electric fuel pump draws in the fuel from the swirl pot (fuel pump relay located in glove box. It pumps the fuel into the fuel filter in the left tank half. The fuel flows from the fuel filter through the feed line to the fuel rail.

Fuel Level Sensors
The fuel tank contains 2 sensors, one in each tank half. The tank sensors operate with float elements, which are attached to a pivoted arm (angle measurement). A specific angle of the sensor joint corresponds to each tank chamber fill level.
The sensor joint incorporates a potentiometer with wipers and resistor paths. Every angle has a specific resistance value. The sensor is supplied with 5 Volts by the instrument cluster and measures the voltage drop by the current resistance on which the wiper is resting.
The voltage drop measured is processed in the instrument cluster as follows:
^ Conversion into a fuel level for the two chambers (on the basis of a comparison table)
^ Display of the fuel level





Fuel Pressure Regulation
Fuel Row: From pressure regulator => suction jet pump in left tank half and suction jet pump in right tank half => swirl pot in right tank half.
The suction-jet pumps direct the fuel from the left and right tank halves into the swirl pot. This ensures that the electric fuel pump always has a sufficient supply of fuel available.
The fuel filter incorporates the pressure regulator. The pressure regulator is a spring loaded diaphragm regulator, which limits the pressure in the fuel feed line to 3.5 bar (for M54).
When the pressure rises above 3.5 bar, the pressure regulator opens a discharge port. The excess fuel flows back through the discharge port into the right tank half (swirl pot) and drives the two suction jet pumps (nonreturn fuel system). The fuel feed line delivers the fuel at 3.5 bar to the fuel rail.