Fuel Delivery and Air Induction: Description and Operation

GF07.61-P-3004MOS 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)
^ Circuit 87M ON (engine control ON)

Fuel supply, general points
In all operating conditions, the fuel supply delivers filtered fuel to the injection valves from the fuel tank, in sufficient quantity and at sufficient pressure (injection pressure).

Fuel supply, function sequence
The description of the fuel supply is subdivided into:
^ Function sequence for fuel pump actuation on engine 275.953
^ Function sequence for fuel pump control on engine 275.982 (AMG)
^ Fuel delivery function sequence

Function sequence for fuel pump actuation on engine 275.953
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 fuel pump control unit detects the current fuel pressure through the voltage signal from the fuel pressure sensor.
The fuel pump control unit evaluates the current fuel pressure, compares it with the preset specified value of 3.8 bar, and actuates the fuel pump with a pulse width modulated signal (PWM) signal as required so that the actual value corresponds to the specified value.

The fuel pump control unit sends the current fuel pressure over the drive train CAN (CAN C) to the ME-SFI control unit.

Function sequence for fuel pump control on engine 275.982 (AMG)
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 signal to the fuel pump control unit. 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.

Depending on the fuel requirements, the fuel pressure is regulated at about 3.6 to 5.0 bar.

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 to the fuel distribution rail (one-line system).

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.

The overflow valve at the fuel filter opens when the fuel pressure is about 3.0 bar. The fuel flow rate is limited to about 50/h by a nozzle in the suction jet pump.
The fuel from the overflow valve is supplied to the suction jet pump in the LH fuel tank chamber an.
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.