SMART Series 451 - Check for very fine leaks

Fuel supply
Fuel system
43
Introduction of the smart fortwo, Model Series 451
Check for very fine leaks
If no fine leak is recognized then purging is briefly
enabled and then the vacuum of about -0.1 psi (-6
mbar) is built up again. The vacuum must not reduce
more rapidly than 0.0014 to 0.002 psi/s (0.1 to 0.15
mbar/s) in the closed system (depends on fuel level).
If the vacuum drops more rapidly, the fault "very fine
leak" will be registered.
The reduction in vacuum depends on the fuel level in
the fuel tank and on outgassing of the fuel. The
outgassing of the fuel is measured just before the test
by the fuel tank pressure sensor and is allowed for
during fault determination.
The test for fine and very fine leaks is aborted if an
excessive lean correction of the lambda control takes
place during the build-up of the vacuum.
The function of the tank vent valve is checked at the
same time by the actuation. If the closed tank vent
valve jams, the fault "gross leak" is stored.
Test requirements
• Engine at idle
• Vehicle stationary
• Drive position "D" or "R" is engaged
• Off-period after engine start elapsed (approx. 16
minutes) or mixture adaptation performed
• Lambda control enabled
• Intake air temperature <113° F (<45 °C)
• Coolant temperature at engine start <212° F (<100
°C)
• Air injection not active
• Air pressure >1.12 psi (>780 hPa) (i.e. no tests
performed above approx. 2735 yd (2500 m)
altitude)
• Low loading of activated charcoal canister
• Fuel level in fuel tank between approx. ¼ and ¾
• No fault in outside air shutoff valve
• No fault in the fuel tank pressure sensor
• No fault in tank vent valve
• Battery voltage > 11 V
The outside air shutoff valve is reopened after the
tests.
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