·---
Fuel evaporation
0
◊
~
D.
23 22
68
27
◊
Evaporative emission canister
The evaporative emission canister consists of a con-
tainer filled with activated charcoal, the task of which
is to "temporarily store" fuel vapours from the tank
and then release the vapours via the purge valve to
the intake manifold for combustion.
The evaporative emission canister thus has a hose
connection both to the fuel tank and to the intake
manifold, but is also connected to the surrounding
air. Air is drawn via this connection with the surround-
ing air through the evaporative emission canister and
brings fuel vapours into the intake manifold with it.
Technical Description 55
+30
230
589
J37
27
J!P
21
µp
321
EVAP canister purge valve
The purge valve consists of a solenoid valve
mounted on the vacuum hose between
th~
evapora-
tive
emission canister and intake manifold after the
throttle.
The valve is supplied with current from the main relay
and controlled from pin 27 of the control module. The
lead is connected to pin 21 of the control module. By
measuring the voltage on pin 21, the control module
determines whether the function is electrically cor-
rect.
An 8 Hz PWM signal is applied to the valve which
starts to work as soon as the closed loop is activated,
engine coolant temperature is above 60°C (140
°F)
and
intake manifold pressure is below 90 kPa.
The control module starts purging by grounding the
circuit to the valve for extremely short periods and
then gradually increasing the duration of the periods.
The reason for this is that the closed loop must be
given time to compensate for the additional fuel. The
valve operates for 41/2 minutes, stops for 1/2 a min-
ute, operates for 4 1/2 minutes, and so on.
Saab 9000
I
To Next Page
Loading...
