Fuel supply
42
Fuel system
Introduction of the smart fortwo, Model Series 451
Fuel supply
A non-return fuel system is used for the fuel supply.
The fuel is pumped by a flow pump via the fuel filter in
the fuel tank into the fuel distributor rail according to
requirements.
Any surplus fuel is pumped via the fuel pressure
regulator straight into the buffer of the fuel pump.
The fuel pressure regulator is designed to ensure
that there is always a pressure of 46 psi (3.24 bar) at
the fuel distributor rail. The fuel tank fill level is
measured by a float-and-lever sensor.
Fuel tank
The fuel tank is located in front of the rear axle under
the seats. It is made of polyethylene and is formed
such that the available installation space is used to an
optimum. The capacity of the fuel tank is 8.72 gallons
(33 liters), including a 1.32 gallon (5 liter) reserve.
The intank fuel supply system consists of a fuel pump
with fuel level sensor, fuel pressure regulator and an
integrated fuel filter.
Evaporative emission control system (purging)
The evaporative emission control system prevents
fuel vapors escaping to the atmosphere. The fuel
vapors are stored in the activated charcoal filter and
then sent later to the engine for combustion.
Leak test
The leak test for the fuel evaporation control system
must detect leaks with a diameter as of 0.02 in (0.5
mm) and must take place in three stages (function
chain):
• Test for gross leaks (equal to or greater than 0.12
in (3 mm))
• Test for fine leaks (equal to or greater than 0.04 in
(1 mm))
• Test for very fine leaks (equal to or greater than
0.02 in (0.5 mm))
Test for gross leaks
The outside air shutoff valve is closed and the tank
vent valve is opened. Intake manifold vacuum present
in fuel tank. This vacuum is measured by the tank
pressure sensor.
If no vacuum is built up in the fuel tank (approx. -0.1
psi (-6 mbar) within approx. 12 seconds) there is a
major leak (e.g. tank cap open, hose line loose).
The test will be interrupted and the "gross leak" fault
will be registered.
If the ME-SFI [ME] control unit detects a system with
a gross leak, the fuel reserve warning lamp in the
instrument cluster flashes and the message "CHECK
FILLER CAP" appears in the multifunction display.
Test for fine leaks
The tank vent valve is closed at a vacuum of around -
0.1 psi (-6 mbar). The system is closed and thereby
airproof. The vacuum is then measured for approx. 30
seconds. The vacuum must not reduce more rapidly
than 0.004 to 0.007 psi/s (0.3 to 0.5 mbar/s) (depends
on fuel level). If the vacuum drops more rapidly, there
is a fine leak.
The test will be interrupted and the "fine leak" fault
will be registered.
SN_Typ 451_us.book Seite 42 Freitag, 30. November 2007 1:56 13
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