Fuel system
Combustion
31b
Introduction of the New V12 Biturbo Engine, M 279 AMG
Fuel supply
The fuel supply system provides the fuel injection
valves with a sufficient quantity of filtered fuel from
the fuel tank as a sufficient pressure under all oper-
ating conditions.
Fuel pump control
The fuel pump is switched on when the ground
signal "Fuel pump ON" transmitted by the ME-SFI
(motor electronics) control unit is received by the
fuel system control unit.
The current fuel pressure is registered by the
ME
-SFI control unit by means of the voltage signal
from the fuel pressure sensor.
To control the fuel pump
the ME-SFI control unit
evaluates the
fuel pressure and the load
requirement and transmits the pulse width
modulated signal (PWM signal) "Specified fuel
pressure" to the fuel system control unit. This
evaluates the PWM signal and actuates the fuel
pump with 3 phase-shifted PWM signals so that the
actual value of the fuel pressure matches the
specified value.
Depending on the fuel requirement, the fuel
pressure is thus varied from
approx. 3.0 to 5.2 bar
(relative).
At engine start the fuel pressure is raised
to 6.0 bar (relative).
Fuel feed
The fuel pump draws the fuel through the fuel
strainer at the bottom of the fuel feed module and
pumps it through the fuel filter with fuel pressure
regulator to the fuel distribution rail (single-line
system, without return line). The fuel pressure
regulator restricts the fuel pressure to approx.
6.2 bar (relative).
The fuel returning from the fuel pressure regulator
flows back into the fuel
feed module and drives a
suction jet pump, which
fills the fuel feed module
with fuel if the fuel level is low.
Safety fuel shutoff
The ME-SFI control unit controls the safety fuel
shutoff on the basis of the following sensors and
signals:
• Crankshaft Hall sensor, engine speed
• Throttle valve actuator, throttle valve position
• Supplemental Restraint System control unit,
direct crash signal
• Supplemental Restraint System control unit,
indi
rect crash signal via chassis CAN 1
The safety fuel shutoff function is activated by the
ME-S
FI contro
l unit under the following conditions:
• Mechanical faults in the throttle valve actuator
• Absence of the engine speed signal
• Crash signal
– This printout will not be recorded by the update service. Status: 06 / 2012 –
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