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

ENGINE 651.9 in MODEL 204, 207, 212 (except 212.098/298), 218 up to model year 2014 

Function requirements for fuel supply, general points 

IMPORTANT From 1.6.12 the fuel system in model 204.9 is being changed over from Delphi to Bosch. One exception is the fuel system high pressure pump which will continue to come from Delphi. The function sequences will not affected by this.

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 on model 204.0/9 up to 05/2009, model 212.0 up to 08/2009 

The CDI control unit (N3/9) actuates the fuel pump (N10/2kD) via the fuel pump relay (M3).

Function sequence for fuel pump actuation on model 204.0/9 as of 06/2009, model 204.2/3, model 207.3/4, model 212.0 as of 09/2009, model 212.2, model 218 

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 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 low-pressure fuel circuit 

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

The fuel system control unit detects the current fuel pressure based on the voltage signal from the fuel pressure sensor (B4/7) (model 204.0/9 as of 06/2009, model 204.2/3, model 207.3/4, 212.0 as of 09/2009, model 212.2) or fuel pressure sensor (B4/7) (model 218) and transmits the information to the CDI control unit via the drive train CAN.

The fuel system control unit evaluates the current fuel pressure, compares it with the specified fuel 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 up to 05/10 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 front SAM control unit with fuse and relay module (N10/1) and heats the fuel in the fuel filter.

The condensation level in the fuel main filter is monitored by means of the fuel filter condensation sensor with heating element. Above a condensation level of about 100 ml the CDI control unit sends a message via the chassis CAN (CAN E) to the instrument cluster (A1) which is displayed as a warning message in the multifunction display (A1p13).

IMPORTANT Fuel preheating as of 06/10

In order to achieve flowability of the fuel at lower outside temperatures a fuel filter condensation sensor with a heating element is fitted with a water level monitoring.

The heating element is actuated by the glow output stage (N14/3) and warms the fuel in the fuel filter. 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 drivetrain LIN (LIN C1) to the CDI control unit. Above a condensation level of ca. 100 ml the CDI control unit sends a message to the instrument cluster via the chassis CAN which is displayed as a warning message in the multifunction display.

IMPORTANT Fuel preheating with code (71o) Retrofitting of a heatable fuel filter In order to achieve flowability of the fuel at lower outside temperatures a fuel filter condensation sensor with a heating element is fitted with a water level monitoring.

The heating element is actuated by the control unit for condensation sensor for fuel filter with heating element (N33/7) and heats the fuel in the fuel filter.

The condensation level monitoring in the fuel filter is by means of the condensation sensor for fuel filter with heating element.

The condensation level is read in by the control unit for condensation sensor for fuel filter with heating element and transmitted to the CDI control unit. Above a condensation level of ca. 100 ml the CDI control unit sends a message to the instrument cluster via the chassis CAN which is displayed as a warning message in the multifunction display.

Shown on fuel low-pressure circuit (except model 204.9 as of 1.6.12) 

Fig 1: Fuel Low-Pressure Circuit Diagram (Except Model 204.9)
G10242075Courtesy of MERCEDES-BENZ USA

Function sequence for high-pressure fuel 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 transmitted continuously to the CDI control unit.

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

View of fuel high-pressure circuit (except model 204.9 as of 1.6.12) 

Fig 2: View Of Fuel High-Pressure Circuit
G10242076Courtesy of MERCEDES-BENZ USA

Function sequence for safety fuel shutoff 

The safety fuel shutoff system is designed to ensure traffic and occupant 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 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 fuel pump relay (model 204.0/9 up to 05/2009, model 212.0 up to 08/2009) or over the drive CAN, or over the fuel system control unit () (model 204.0/9 as of 06/2009, model 204.2/3, model 207.3/4., model 212.0 as of 09/2009, model 212.2, model 218).

  Electrical function schematic for fuel supply MODEL 204 PE07.10-P-2703-97FAE
MODEL 207 PE07.10-P-2703-97EAE
MODEL 212 PE07.10-P-2703-97DAE
Model 218 PE07.10-P-2703-97XAD
  Electrical function schematic for safety fuel shutoff MODEL 204 PE07.10-P-2733-97FAE
MODEL 207 PE07.10-P-2733-97EAE
MODEL 212 PE07.10-P-2733-97DAE
Model 218 PE07.10-P-2733-97XAD
  Overview of system components for common rail diesel injection (CDI)   GF07.16-P-9997OM
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