Fuel system
32
Combustion
b
Introduction of the New V12 Biturbo Engine, M 279 AMG
Fuel pressure regulator
The fuel pressure regulator limits the fuel pressure
by adjusting the fuel return quantity. When the set
fuel pressure is exceeded, the diaphragm in the fuel
pressure regulator is pressed against the
compression spring and the valve attached to the
diaphragm opens the hole for the fuel return.
When the fuel pressure drops below the set
pressure, the valve is closed again by the
co
mpression spring.
Fuel filter
The fuel filter element is integrated into a plastic
housing. The fuel flows through from the outside to
the inside. Impurities are trapped by the filter.
There is a check valve in the feed point of the fuel
filter which prevents reduction of the fuel
pressure
when the fuel pump is switched off.
Purging
Fuel vapors must not be allowed to escape into the
atmosphere when the fuel tank is vented.
The fuel vapors are stored in the activated charcoal
canister and later burned in
the engine.
When the engine is running, the fuel vapors stored
in the activated charcoal canister are drawn off via
the purge switchover valve and burned in
the
engine.
To regulate the purge quantity, the switchover valve
is actuated by the ME-SFI control un
it at the ground
end by means of a PWM signal with a frequency of
10 Hz to 30 Hz.
The constant opening and closing of the purge
switchover valve with on/off cycles of varying
lengths determine
the purge quantity.
Purging
(with code (494) USA version)
Activated charcoal canister shutoff valve
The activated charcoal canister shutoff valve is
actuated by the ME-SFI control unit to close the
vent
ilation connections of the activated charcoal
filter. This is necessary in order to perform the leak
test of the purging system that is required by law.
When the activated charcoal canister shutoff valve
is closed, the mechanical safety
valve
is responsible
for ventilating the activated charcoal filter.
OBD pressure sensor
The OBD pressure sensor registers the internal
pressure in the fuel tank for the leak test. The OBD
pressure sensor is located on the purge line below
the filler neck.
i Note
The idle speed control function prevents the
purging proces
s from causing changes to the
engine speed at idle. The fuel/air mixture is
leaned out accordingly depending on the amount
of fuel vapor in the activated charcoal canister.
– This printout will not be recorded by the update service. Status: 06 / 2012 –
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