Fuel Supply, Function - GF07.10-S-1003TRC
Engine 274 in model 447, 448
except code XM0 (Facelift)
Function requirements for fuel supply, general points
- Circuit 87M ON (Engine management ON)
- Circuit 15 ON (ignition ON)
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 system high pressure pump (19).
Function sequence for fuel supply
The function sequence for fuel supply is described in the following steps:
- Function sequence for fuel low-pressure circuit
- Function sequence for fuel system high-pressure circuit
- Function sequence for safety fuel shutoff
Function sequence for fuel low-pressure circuit
Switching on of the fuel pump with fill level sensor (M3/6) takes place if a signal "fuel pump ON" is received by the FSCU (FSCU) (N118). This signal is sent redundantly from the ME-SFI [ME] control unit (N3/34) as a CAN signal via the drive train CAN (CAN C) and as a ground signal.
The fuel system control unit (FSCU) (N118) 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 over the fuel pressure and temperature sensor (B4/21) and transmits this information via the drive train CAN (CAN C) to the FSCU (FSCU) (N118).
The FSCU (N118) evaluates the current fuel pressure, compares it with the fuel specified pressure and actuates the fuel pump with fill level sensor (M3/6) in such a way that the actual value corresponds to the specified value.
In order to determine the fuel specified pressure (fuel requirements), the ME-SFI [ME] control unit (N3/34) evaluates the fuel pressure and the load requirement. The fuel delivery volume is regulated variably from 0 to 130 l/h for a fuel pressure of about 4 to 6.7 bar according to the fuel requirements.
For actuation the fuel pump suctions with fill level sensor (M3/6) the fuel from the fuel feed module and pumps it through the fuel filter to the fuel system high pressure pump (19) (single line system without return line).
The overflow valve in the fuel filter opens at a fuel pressure from approx. 7 to 9 bar.
There is a check valve in the feed line to the fuel filter which prevents reduction of the fuel pre-delivery for a switched off fuel pump with fill level sensor (M3/6) (down to below approx. 4.5 bar).
Function sequence for fuel system high-pressure circuit
In the fuel high-pressure circuit the required fuel pressure for spray guided direct injection is generated, regulated and in the rail (20).
The ME-SFI [ME] control unit (N3/34) directly reads in to regulate the fuel pressure of pressure and the temperature signal of the fuel pressure and temperature sensor (B4/21).
The description of the fuel high-pressure circuit is subdivided into:
- Fuel feed
- Fuel pressure control
Fuel feed
The fuel system high pressure pump (19) compresses the fuel (depending on the operating condition) and routes it over the high-pressure line and the rail (20) to the fuel injectors (Y62).
At the fuel system high pressure pump (19) there is a quantity control valve (Y94) which regulates the fuel quantity which is fed to the pump element in the fuel system high pressure pump (19) dependent on the requirements and a characteristics map. Actuation of the quantity control valve (Y94) takes place via a PWM signal from the ME-SFI [ME] control unit (N3/34).
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 about 200 bar.
The pressure is only lowered for standstill of the vehicle to 130 bar in order to reduce the noise emissions of the fuel system high pressure pump (19).
In the case of shutting off a vehicle with a hot engine, the fuel pressure can increase up to 250 bar (+17 bar) in the fuel high-pressure circuit. Upon reaching this threshold a pressure limiting valve opens in the fuel system high pressure pump (19) and the pressure is reduced. Upon starting the engine the pressure falls rapidly to the normal operating pressure of bar.
During regulation of the fuel high-pressure circuit one differentiates between the following operating conditions:
- Start
- Normal mode
- Low-pressure limp-home mode (fuel high pressure is not reached)
- Stop
Start
- The quantity control valve (Y94) is energized and closed, so there is full delivery from the fuel system high pressure pump (19) and rapid pressure buildup
Normal mode
- The quantity control valve (Y94) regulates the supplied and the required fuel quantity over the duty cycle
Low-pressure limp-home mode (fuel high pressure is not reached)
- The quantity control valve (Y94) is de-energized and therefore opened
- Actuation of fuel injectors (Y62) extended
- Reduced performance, max. speed approx. 70 km/h
Stop
- Quantity control valve (Y94) is de-energized and opened.
- Fuel pump with fill level sensor (M3/6) is not actuated
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 (N3/34) controls the safety fuel shutoff system on the basis of the following assembly parts and signals:
- Crankshaft Hall sensor (B70/2), engine rpm
- Throttle valve actuator (M16/50), throttle valve position
- Supplemental restraint system control unit (SRS) (N2/18), direct crash signal
- Supplemental Restraint System control unit (SRS) (N2/18), indirect crash signal via chassis CAN (CAN E)
The safety fuel shutoff is activated by the ME-SFI [ME] control unit (N3/34) for the following conditions:
- Mechanical fault in throttle valve actuator (M16/50)
- Absence of the engine speed signal
- Crash signal
Mechanical fault in throttle valve actuator (M16/50)
When evaluating the throttle valve position, if the ME-SFI [ME] control unit (N3/34) detects a mechanical fault in the throttle valve actuator (Y62/50), engine speed is limited to about 1200 rpm at idle and about rpm in driving mode by shutting off the fuel injectors (M16).
Absence of the engine speed signal
If the engine speed signal is missing from ME-SFI [ME] control unit (N3/34), the fuel pump with fill level sensor (M3/6) is switched off over FSCU (FSCU) (N118).
Crash signal
If the ME-SFI [ME] control unit (N3/34) received a crash signal indirectly via the chassis CAN (CAN E) or directly from Supplemental Restraint System control unit (SRS) (N2/18), switches the fuel pump with fill level sensor (M3/6) off over the FSCU (FSCU) (N118) (directly and via the drive train CAN (CAN C)) and actuates the quantity control valve (Y94) in order to make the fuel system unpressurized.
| Electrical function schematic for fuel supply | Engine 274 in model 448 except code XM0 (Facelift) |
PE07.10-S-2703-97VDC | |
| Engine 274 in model 447 except code XM0 (Facelift) |
PE07.10-S-2703-97TRC | ||
| Electrical function schematic for safety fuel shutoff | Engine 274 in model 448 except code XM0 (Facelift) | PE07.10-S-2733-97VDC | |
| Engine 274 in model 447 except code XM0 (Facelift) |
PE07.10-S-2733-97TRC | ||
| Overview of system components for gasoline injection and ignition system with direct injection | GF07.70-S-9998TRC |