Fuel Delivery and Air Induction: Description and Operation

GF07.61-P-3004MOR 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
The fuel supply provides the injection valves with filtered fuel from the fuel tank in operating conditions, in sufficient quantity and at sufficient pressure (injection pressure).

Fuel supply, function sequence
The description of the fuel supply is subdivided into:
^ Fuel pump control function sequence
^ Fuel delivery function sequence

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

To control the fuel pump, the ME-SFI control unit evaluates the load requirement and sends the "specified fuel pressure" PWM signal, with a duty cycle of 10 to 90 %, to the fuel pump control unit. This control unit evaluates the PWM signal and the current fuel pressure through the fuel pressure sensor and actuates the fuel pump accordingly, 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 for engine 275.954, and 4.1 bar for engine 275.981 (AMG).

Fuel delivery function sequence
The fuel pump draws fuel through the fuel strainer 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 about 3.8 or 4.1 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.

A restrictor reduces the rate of fuel flow in the fuel return line to about 50 l/h. So that the fuel pressure of about 4.1 (for engine 275.954) or 4.4 bar (for engine 275.981 (AMG)) is not exceeded, the pressure is limited by the pressure limiting valve.