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

ENGINES 642.8 in MODEL 164.1 as of model year 2009/YoM 08 model refinement package 

ENGINES 642.8 in MODEL 164.8, 251.1 as of model year 2009/YoM 08 

ENGINES 642.8 in MODEL 251.0/1 as of model year 2011/YoM 10 model refinement package 

Function requirements for fuel supply, general points 

Fuel supply, general 

The fuel supply supplies filtered fuel out of the fuel tank in adequate quantities 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 Operation steps:

Function sequence for fuel pump actuation 

The CDI control unit (N3/9) actuates the fuel pump (M3) via the fuel pump relay (F4kO).

At "circuit 15 ON" the fuel pump is actuated by the fuel pump relay integrated into the rear SAM control unit (N10/8) for approx. 20 to 25 s.

When the engine is started ("circuit 50 ON") and when engine running is detected ("circuit 61 ON"), the CDI control unit actuates the fuel pump through the fuel pump relay integrated in the rear SAM control unit, and the fuel pump delivers fuel through the fuel main filter to the high-pressure pump.

Function sequence for low-pressure fuel circuit 

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

Upon 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.

The fuel pressure is regulated variably over pressure limiting valve integrated in the high-pressure pump to about 4.0 to 4.5 bar according to fuel requirements.

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 for model 164.1/8 as of 01.07.10 and for model 251.1 as of 01.08.10

In order to achieve flowability of the fuel at lower outside temperatures a condensation sensor for fuel filter with 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 main filter.

The condensation level in the fuel main filter is monitored by means of the condensation sensor for fuel filter 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 engine compartment CAN which is displayed as a warning message in the multifunction display.

IMPORTANT Fuel preheating system for model 164.1/8 up to 30.06.10 and for model 251.1 up to 31.07.10

To ensure flowability of the fuel at low outside temperatures, vehicles except code (U41) Fuel/water separator and lubrication package are fitted with a fuel preheating system heating element (R54). This heating element is supplied with current via the engine circuit 87 relay (F58kD). Vehicles with code (U41) Fuel/water separator and lubrication package or except code (U42) BlueTec (SCR) diesel exhaust gas cleaning are fitted with a condensation sensor for fuel filter with heating element (B76/1) for water level monitoring. This heating element is supplied with current via the circuit 15 relay (F58kH). The condensation level in the fuel main filter is monitored by the condensation sensor for fuel filter with heating element. Above a condensation level of approx. 100 ml the CDI control unit sends a message via the engine compartment CAN (CAN C) to the IC (A1), which is displayed as a warning message in the multifunction display (A1p13).

IMPORTANT Heating of the fuel for code (71o) Retrofitted heated fuel filter In order to achieve flowability of the fuel at lower outside temperatures a condensation sensor for fuel filter with 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 in the fuel main filter is monitored 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 engine compartment CAN which is displayed as a warning message in the multifunction display.

View of low-pressure fuel circuit 

Fig 1: View Of Low-Pressure Fuel Circuit
G10119997Courtesy of MERCEDES-BENZ USA

Function sequence for high-pressure circuit 

The high-pressure circuit consists of the following components:

The high-pressure pump delivers the fuel into the left rail depending on the signal from the accelerator pedal sensor (B37), the engine speed and the fuel temperature and, at the same time, from there into the right rail. The fuel passes from the respective rail via the high pressure lines to the fuel injectors.

The fuel injectors inject finely atomized fuel selectively into each cylinder.

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, passed on permanently to the CDI control unit and limited to a maximum of 1800 bar by the pressure regulator valve.

View of the high-pressure fuel circuit 

Fig 2: View Of High-Pressure Fuel Circuit
G10119998Courtesy 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:

D Absence of the engine speed signal 

D Crash signal 

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 indirectly receives a crash signal via the engine compartment CAN or directly from the restraint system control unit, it switches the fuel pump off.

REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic for fuel supply Model 164 PE07.10-P-2703-97MAA
Model 251 PE07.10-P-2703-97RAA
REFER TO SYSTEM WIRING DIAGRAMS Electrical function schematic for safety fuel shutoff Model 164 PE07.10-P-2733-97MAA
Model 251 PE07.10-P-2733-97RAA
  Component description for restraint systems control unit N2/7 GF91.60-P-4048GM
  Component description for CDI control unit N3/9 GF07.16-P-6000OGU 
  Component description for rear SAM control unit N10/8 GF54.21-P-7030GM
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