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Fuel Supply, Function - GF07.10-S-1003TRJ

Engine 274 in model 447.6/7 

with code XM0 (Facelift) 

Function requirements for fuel supply, general points 

Fuel supply, general points 

The fuel supply system provides the fuel high-pressure pump (19) with a sufficient quantity of filtered fuel from the fuel tank at sufficient pressure 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 low-pressure circuit 

The fuel pump with fuel delivery module (M3/3) is switched on if a "fuel pump ON" signal is received by the following control unit:

This signal is transmitted redundantly by the ME-SFI [ME] control unit (N3/34) as a CAN signal via the drive CAN (CAN C) and as a ground signal.

The fuel system control unit (FSCU) also receives the CAN signal "Fuel specified pressure" from the ME-SFI [ME] control unit (N3/34).

The ME-SFI [ME] control unit (N3/34) detects the current fuel pressure via the fuel pressure and temperature sensor (B4/21) and transmits this information to the fuel system control unit (FSCU).

The fuel system control unit (FSCU) evaluates the current fuel pressure, compares it with the fuel specified pressure and accordingly actuates the fuel pump with fuel delivery module so that the actual pressure corresponds to the specified pressure.

In order to determine the fuel specified pressure (fuel requirements), the ME-SFI [ME] control unit evaluates the fuel pressure and load requirements. Depending on the fuel requirement, the fuel delivery rate is thus variably regulated between 0 and 130 l/h for a fuel predelivery pressure of approx. 4 to 6.7 bar.

In the case of actuation, the fuel pump with fuel delivery module intakes the fuel from the fuel delivery module and pumps it through the fuel filter to the fuel high-pressure pump (19) (single-line system, without return line).

The overflow valve in the fuel filter opens at a fuel pressure of approx. 7 to 9 bar.

In the feed of the fuel filter, there is a check valve that prevents a decrease of the fuel predelivery pressure (to below approx. 4.5 bar) in the case of a deactivated fuel pump with fuel delivery module.

High-pressure fuel circuit 

G16500813Courtesy of MERCEDES-BENZ USA

Function sequence for fuel high-pressure circuit 

In the high-pressure fuel circuit, the fuel pressure required for the direct injection is generated, regulated and stored in the rail (20).

The ME-SFI [ME] control unit directly reads in the pressure and temperature signal of the fuel pressure and temperature sensor (B4/21) for the regulation of the fuel pressure.

The description of the high-pressure fuel circuit is subdivided into:

Fuel feed 

The fuel high-pressure pump (19) compresses the fuel (depending on the operating status) and routes it via the high-pressure line and the rail (20) to the fuel injectors (Y62).

At the fuel high-pressure pump (19), there is a quantity control valve (Y94) that regulates the fuel quantity that is supplied to the pump element in the fuel high-pressure pump (19) in an as-required and map-dependent manner. The quantity control valve (Y94) is actuated via a pulse width modulated signal of the ME-SFI [ME] control unit.

The fuel pressure and temperature sensor (B4/21) detects the current fuel pressure as well as the temperature of the fuel in the rail (20). The operating pressure is approx. 200 bar.

Solely at vehicle stillstand is the pressure reduced to 130 bar to reduce the noise emission of the fuel high-pressure pump (19).

If a vehicle with hot engine is switched off, the fuel pressure can increase up to 250 bar (+ 17 bar) in the high-pressure fuel circuit. When this threshold is reached, a pressure limiting valve in the fuel high-pressure pump (19) opens and the pressure is reduced. Upon starting the engine the pressure falls rapidly to the normal operating pressure of bar.

A differentiation is made between the following operating states during the regulation of the high-pressure fuel circuit:

Start 

Normal mode 

Low-pressure limp-home mode (fuel high pressure is not reached) 

Stop 

IMPORTANT The high pressure fuel lines made out of stainless steel can be reused after checking. More information on this is available in the repair instructions.

Function sequence for safety fuel shutoff 

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

The ME-SFI [ME] control unit controls the safety fuel shutoff based on the following components and signals:

The safety fuel shutoff is activated by the ME-SFI [ME] control unit for the following conditions:

Mechanical fault in the throttle valve actuator 

If the ME-SFI [ME] control unit detects a mechanical fault in the throttle valve actuator (M16/50) due to the evaluation of the throttle valve position, the engine speed is limited to approx. 1200 rpm in idle and during vehicle operation via the deactivation of the fuel injectors (Y62).

Absence of the engine speed signal 

If the engine speed signal generated by the ME-SFI [ME] control unit is missing, the fuel pump with fuel delivery module is deactivated via the fuel system control unit (FSCU).

Crash signal 

If the ME-SFI [ME] control unit receives a crash signal indirectly via the CAN or directly from the Supplemental Restraint System control unit (SRS) (N2/18), it switches on the fuel pump with fuel delivery module via the fuel system control unit (FSCU) and actuates the quantity control valve (Y94) to depressurize the fuel system.

  Function schematic for fuel supply system   PE47.00-S-2500-97TRL
  Overview of system components for gasoline injection and ignition system with direct injection   GF07.70-S-9998TRJ 
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