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Fuel Supply, Function - GF07.10-P-1003OGF

ENGINE 642.8 in MODEL 166 

as of model year 2016 

ENGINE 642.8 in MODEL 292 

Function requirements for fuel supply, general points 

Fuel supply, general points 

The fuel supply provides an adequate quantity of filtered fuel from the fuel tank to the fuel injectors for cylinders 1 to 6 (Y76/1 to Y76/6) at an adequate pressure and under all operating conditions.

Function sequence for fuel supply 

The function sequence for fuel supply is described in the following steps:

Function sequence for fuel pump actuation 

To switch on the fuel pump (M3) the CDI control unit (N3/9) sends the "Fuel pump ON" signal to the fuel system control unit (N118). This signal is sent redundantly from the CDI control unit as a CAN signal via the drive train CAN (CAN C) and as a ground signal. The fuel system control unit also receives the CAN signal "Fuel specified pressure" from the CDI control unit.

Function sequence for fuel low-pressure circuit 

The fuel low-pressure circuit consists of the following components:

The fuel system control unit detects the current fuel pressure by means of a voltage signal from the fuel pressure sensor (B4/7) and sends this information via drive train CAN to the CDI control unit.

The fuel system control unit evaluates the current fuel pressure, compares it with the fuel specified pressure and actuates the fuel pump accordingly by means of a pulse width modulated signal in such a way that the actual value corresponds to the specified value. During actuation the fuel pump suctions the fuel out of the fuel feed module and pumps it through the fuel filter to the fuel system high pressure pump. Depending on the fuel requirement, the fuel pressure is regulated to about 4.0 bar through the pressure limiting valve integrated into the fuel high-pressure pump.

The quantity control valve also regulates the supply of fuel to the fuel system high pressure pump (feed quantity) depending on the engine operating point in order to keep the fuel temperature low.

IMPORTANT The leak fuel and fuel that is not required are fed back to the fuel tank via the return line.

IMPORTANT Fuel preheating system

In order to achieve flowability of the fuel at low outside temperatures, a fuel filter condensation sensor with heating element (B76/1) for water level monitoring is installed. The heating element is energized by the glow output stage (N14/3) and heats the fuel in the fuel filter.

Condensation level monitoring in the fuel filter is by means of the condensation sensor.

The condensation level is read in by the glow output stage and passed on via the drive train LIN (LIN C1) to the CDI control unit. As of a condensation level of approx. 100 ml, the CDI control unit sends a message via chassis CAN 1 (CAN E1), electronic ignition lock control unit (N73) and chassis CAN 2 (CAN E2) to the instrument cluster (A1) that is shown as a warning message in the multifunction display (A1p13).

Shown on fuel low-pressure circuit 

G11973192

Function sequence for fuel system high-pressure circuit 

The fuel high-pressure circuit consists of the following component:

Dependent on the signal received from the accelerator pedal sensor (B37), the engine speed and the fuel temperature, the fuel system high pressure pump delivers fuel to the left rail and from there simultaneously to the right rail.

The fuel passes from the respective rail via the high-pressure lines to the fuel injectors. The fuel injectors spray fuel in a fine atomized form. The CDI control unit calculates the injection quantity selectively for each cylinder based on a characteristics map for the respective operating condition. The injection quantity is dependent upon the fuel pressure in the rail and the actuation duration of fuel injectors.

The fuel pressure in the rail is controlled by the pressure regulating valve and quantity control valve. The actual applied fuel pressure in the rail is detected by the fuel pressure sensor and is limited by the pressure regulating valve to a maximum of 1800 bar. The fuel temperature is detected over the fuel temperature sensor. Both pieces of information are passed on permanently to the CDI control unit.

Shown: fuel high-pressure circuit 

G11973193

Function sequence for safety fuel shutoff 

The safety fuel shutoff system is designed to ensure traffic and passenger safety.

The CDI control unit controls the safety fuel shutoff on the basis of the following signals:

The safety fuel shutoff is activated by the CDI control unit in the following conditions:

Absence of the engine speed signal 

If the engine speed signal generated by the CDI control unit is missing the fuel pump will be switched off.

Crash signal 

If the CDI control unit receives a crash signal indirectly via chassis CAN 1 or directly from the SRS control unit, it switches off the fuel pump, the quantity control valve and the pressure regulating valve, and briefly actuates the fuel injectors to depressurize the fuel system.

  Electrical function schematic for fuel supply   PE07.10-P-2703-97NBD
  Electrical function schematic for safety fuel shutoff   PE07.10-P-2733-97NBD
  Overview of system components for common rail diesel injection (CDI)   GF07.16-P-9997OGF 
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