Fuel Delivery and Air Induction: Description and Operation

GF07.61-P-3004MAS ME Fuel Supply, Function
- as of model year 09

Component Identification:

Function requirements for fuel supply, general points
^ Circuit 15 ON (ignition ON)
^ "Fuel pump ON" ground signal

Fuel supply, general points
The fuel supply system makes an adequate quantity of filtered fuel from fuel tank available to fuel injectors for all operating conditions and at an adequate pressure (injection pressure).

Fuel supply, function sequence
The fuel supply function sequence is divided into the following points:
^ Fuel pump control function sequence
^ Fuel delivery function sequence

Fuel pump control function sequence
The fuel pump is switched on if the fuel pump control unit (N118) receives the "fuel pump ON" ground signal from the ME-SFI control unit (N3/10).

The ME-SFI control unit detects the current fuel pressure through the voltage signal from the fuel pressure sensor.
To control the fuel pump, the ME-SFI control unit evaluates the fuel pressure and load requirement and sends the "specified fuel pressure" PWM (pulse width modulated) signal to the fuel pump control unit (with a duty cycle of 10 to 90 %). This control unit evaluates the PWM signal and actuates the fuel pump with 3 phase shifted PWM signals as required, so that the actual fuel pressure value corresponds to the specified value.
The fuel pressure is regulated to be variable from between 4.6 and 5.5 bar depending on the fuel pressure.

Fuel delivery function sequence
The fuel pump draws fuel from the bottom of the fuel feed module through a fuel strainer, and pumps it through the fuel filter into the fuel distribution rail (one-line system).
The fuel pressure is limited by the pressure limiting valve to about 6.5 bar.

The fuel line to the fuel filter has a check valve, which prevents the fuel pressure from falling when the fuel pump is switched off.

A junction in the fuel line upstream of the fuel filter supplies part of the fuel feed to the suction jet pump in the LH fuel tank chamber. This suction jet pump delivers fuel from the LH fuel tank chamber into the fuel feed module (RH fuel tank chamber) and thus prevents the fuel tank from being emptied on one side only.