Subaru 1600 Service Manual page 182

EMISSION CONTROL SYSTEM
Air cleaner
Fig. 5-26 A I system
Secondary air inlet
Secondary air outlet
A1o.188
Fig.
5-27 ASV III without cutoff valve
3) Non4WD of non-Califomia
models
1) Component parts
• Two ASVIs with cutoff valve
• ASV II without cutoff valve
• Air suction pipes
• Air introduction hoses
• Silencers
• Air cleaner
• Thennosensor
• Solenoid valve I
• Check valve II
• ECM
Secondary air is supplied to the
exhaust ports on # 1-#3 and #2-#4
cylinders sides by ASV with cutoff
valve.
Also the secondary air is supplied to
the exhaust port near the up stream
portion of oxidation catalyst by ASV
without cutoff valve that is installed
on rear exhaust pipe.
2) Operational principle
The exhaust gas pulsation is trans-
Air induction
hose
A10·187
mitted to the air suction valve (a kind
of check valve having reed valves)
through the air suction pipe.
When the negative pressure of pulsa-
tion is transfered to the ASV, the
reeds of air suction valve are opened
and simultaneously fresh air from the
air cleaner is sucked by itself into the
exhaust passage.
When, on the other hand, the positive
pressure reaches the ASV, the reeds
1
Electronic control mod ule
2
Solenoid valve I
3 Check valve II
4 Air ind uction hose
5 Thermosensor
6 Air cleaner
1 Silencer
8 Air induction hose
Fig. 5-28 AI system
are closed to prevent the adverse flow
of exhaust gas.
An ASV without cutoff valve always
operates regardless of coolant tempera-
ture and ECM signal. On the other
hand, two ASVs with cutoff valves are
controlled both by coolant tempera-
ture sensed by the thennosensor and
time governed by the ECM.
When the coolant temperature is below
35°C (95°F), the ECM gives a com-
mand to open the intake manifold
vacuum passage of the solenoid valve I
for the period of
123
seconds, where-
by the two cutoff valves being opened
by the diaphragm vacuum actuator to
operate the two ASV s.
Under such driving condition as wide-
open-throttle acceleration, the check
valve closes the vacuum circuit to
confine the vacuum so as to hold the
cutoff valve open for that period.
After the period, the ECM gives a
command to close the vacuum passage
of the solenoid valve and open the
atmospheric pressure passage, then the
vacuum in the vacuum chambers of
the cutoff valves goes out through the
solenoid valve
I, whereby the two
cutoff valves being closed to deactivate
the two ASV s.
9 Air suction valve I with cutoff valve
10 Air suction pipe
11
Air suction valve II
12 Silencer
13 Air suction pipe
14 Silencer
15 Air induction hose
16 Air suction valve I with cutoff valve
A10-189