Fuel Delivery and Air Induction: Description and Operation

GF07.61-P-3004MAR ME Fuel Supply, Function
- refinement package
- 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 steps:
^ Fuel pump control function sequence
^ Fuel delivery function sequence

Fuel pump control function sequence
The fuel pump is actuated by the ME-SFI control unit (N3/10) through the fuel pump control unit (N118).
The fuel pump control unit is switched on through the fuel pump relay (K40/5kT).

The ME-SFI control unit detects the current fuel pressure through 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 signal (pulse width modulated signal), with a duty cycle of 10 to 90 %, to the fuel pump control unit. This control unit evaluates the PWM signal and actuates the fuel pump in single-phase, so that the actual fuel pressure value corresponds to the specified value.

Depending on the fuel requirements, the delivery rate of the fuel pump is controlled at a constant fuel pressure of about 3.8 bar.

Fuel delivery function sequence
The fuel pump draws fuel from the bottom of the swirl pot and pumps it through the fuel filter with integrated fuel pressure regulator to the fuel distribution rail (single-line system). The fuel pressure is limited to 3.8 bar by the fuel pressure regulator.

The fuel return from the fuel pressure regulator supplies a suction jet pump, which is used to fill the swirl pot.

The restrictor reduces the rate of fuel flow in the fuel return line to about 50 l/h. The fuel pressure is limited by the pressure limiting valve so that a pressure of about 4.1 bar is not exceeded,.