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Fuel supply, function - GF07.10-P-1003OGA

ENGINE 642.8 in MODEL 207 as of 6/1/13, 212, 218 as of model year 2014 

Function requirements for fuel supply, general points 

Fuel supply, general points 

The fuel supply supplies filtered fuel out of the fuel tank in adequate amounts under all operating conditions at an adequate pressure to the fuel injectors (Y76).

Function sequence for fuel supply 

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

Function sequence for fuel pump actuation 

Switching on of the fuel pump takes place when a signal "fuel pump ON" is received by the fuel system control unit (N118). This signal is sent redundantly from the CDI control unit (N3/9) 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 "Specified fuel 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 based on a voltage signal from the fuel pressure sensor (B4/7) (model 207, model 212) or the fuel pressure sensor (B4/7) (model 218), and it sends this information over the 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 with a pulse width modulated signal (PWM signal) as required such 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 main filter to the high-pressure pump. Depending on the fuel requirement, the fuel pressure is regulated to about 4.0 bar via the pressure limiting valve integrated in the high-pressure pump.

In addition, the quantity control valve regulates the supply of fuel to the high-pressure pump 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 guarantee the flowability of the fuel at low outside temperatures, engine 642.8 is fitted with a fuel filter condensation sensor with heating element (B76/1) for water level monitoring.

On engines with engine timing CR60 and CR61 the heating element is energized by the glow output stage (N14/3) and heated by the fuel in the fuel filter. The CDI control unit receives the information on the condensation level via the glow output stage and the drive LIN (LIN C1) by the fuel filter condensation element.

As from a condensation level of approx. 100 ml, the CDI control unit sends a message over chassis CAN 1 to the front SAM control unit with fuse and relay module (N10/1). The front SAM control unit with fuse and relay module forwards the message over chassis CAN 2 to the instrument cluster (A1), the message is then shown on the multifunction display (A1p13) as a warning message.

IMPORTANT The instrument cluster receives these messages over chassis CAN 2 (CAN E2), routed from the front SAM control unit with fuse and relay module, which receives the messages on chassis CAN 1 (CAN E1) from the CDI control unit.

View of fuel system 

Fig 1: View Of Fuel System
G10242073Courtesy of MERCEDES-BENZ USA

Function sequence for fuel system high-pressure circuit 

The high-pressure circuit consists of the following components:

Depending on the signal received from the accelerator pedal sensor (B37), the engine speed and the fuel temperature, the 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 effectively applied fuel pressure in the rail is detected by the rail pressure sensor, continuously passed on to the CDI control unit and limited to a maximum of 1600 bar by the pressure regulating valve.

View of the fuel high-pressure circuit 

Fig 2: View Of Fuel High-Pressure Circuit
G10242074Courtesy of MERCEDES-BENZ USA

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 sensors and 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 the chassis CAN 1 or directly from the Supplemental Restraint System control unit, it switches off the fuel pump, the quantity control valve and the pressure regulating valve and actuates the fuel injectors briefly in order to depressurize the fuel system.

IMPORTANT Fuel pump actuation

Over the drive train CAN from the fuel system control unit.

  Electrical function schematic for fuel supply Model 207 PE07.10-P-2703-97EAJ
  Electrical function schematic for fuel supply Model 212 PE07.10-P-2703-97DAM
  Electrical function schematic for fuel supply Model 218 PE07.10-P-2703-97XAE
  Electrical function schematic for safety fuel shutoff Model 207 PE07.10-P-2733-97EAJ
  Electrical function schematic for safety fuel shutoff Model 212 PE07.10-P-2733-97DAM
  Electrical function schematic for safety fuel shutoff Model 218 PE07.10-P-2733-97XAE
  Overview of system components for common rail diesel injection (CDI)   GF07.16-P-9997OG
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