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

ENGINE 651.9 in MODEL 207, 212 (except 212.098/298), 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 (M3) takes place when the 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 "Fuel specified pressure" signal over the drive train CAN 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, 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 filter to the high-pressure pump.

The fuel pressure is regulated variably to about 4.0 bar according to the fuel requirements via the pressure limiting valve integrated in the high-pressure pump.

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

IMPORTANT The maximum feed volume at 12 V supply voltage and a charged fuel filter is:

IMPORTANT On engines 651.913 and 651.925 the fuel leaking from the fuel injectors (solenoid injectors) is sucked into the high pressure pump through the venturi nozzle. 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 actuated by the glow output stage (N14/3) and warms the fuel in the fuel filter.

IMPORTANT The condensation level in the fuel main filter is monitored by means of the fuel filter condensation sensor with heating element. The condensation level is read in by the glow output stage and sent via the drive train LIN (LIN C1) to the CDI control unit.

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 SAM control unit sends a signal over the chassis CAN 2 (CAN E2) to the instrument cluster (A1), which is shown on the multifunction display (A1p13) as a warning message.

Shown on fuel low-pressure circuit 

Fig 1: Fuel Low-Pressure Circuit Diagram
G10242077Courtesy of MERCEDES-BENZ USA

Function sequence for fuel system high-pressure circuit 

The high-pressure circuit consists of the following components:

The high-pressure pump pumps the fuel into the rail according to the signal from the accelerator pedal sensor (B37) and the engine speed. From the rail, the fuel flows through 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 depends on the fuel pressure in the rail and the actuation time of the fuel injectors.

The fuel pressure in the rail is controlled by the pressure regulating valve and quantity control valve. The fuel pressure actually present in the rail is measured by the rail pressure sensor and sent continuously to the CDI control unit.

The fuel temperature is measured by the fuel temperature sensor and transmitted continuously to the CDI control unit.

Function sequence for safety fuel shutoff 

Fig 2: Safety Fuel Shutoff System Diagram
G10242078Courtesy 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 over chassis CAN 1 or directly from the Supplemental Restraint System control unit (model 204) and Supplemental Restraint System control unit (model 207, 212, 218), it switches off the following components:

IMPORTANT Fuel pump actuation

Over the drive train CAN and over the fuel system control unit.

  Electrical function schematic for fuel supply MODEL 207 PE07.10-P-2703-97EAN
  Electrical function schematic for fuel supply MODEL 212 PE07.10-P-2703-97DAR
  Electrical function schematic for fuel supply MODEL 218 PE07.10-P-2703-97XAH
  Electrical function schematic for safety fuel shutoff MODEL 207 PE07.10-P-2733-97EAN
  Electrical function schematic for safety fuel shutoff MODEL 212 PE07.10-P-2733-97DAR
  Electrical function schematic for safety fuel shutoff MODEL 218 PE07.10-P-2733-97XAH
  Overview of system components for common rail diesel injection (CDI)   GF07.16-P-9997OM
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