Subaru XT 1988 Service Manual page 134

EMISSION CONTROL SYSTEM AND VACUUM FITTING
2-1
Crankcase Emission Control
System
DESCRIPTION
The positive crankcase ventilation (PCV) system is employed
to prevent air pollution which will be caused by blow-by gas
being emitted from the crankcase.
The system consists of a sealed oil filler cap, rocker covers
with an emission outlet and fresh air inlet, connecting hoses,
PCV valve and an air cleaner.
At the part throttle, the blow-by gas in the crankcase flows
into the intake manifold through the connecting hose of
rocker cover on
#2/#4
side, connecting hose of crankcase and
PCV valve by the strong vacuum of the intake manifold.
Under this condition, the fresh air is introduced into the
crankcase through connecting hose of rocker cover on #1/#3
side, and drawn to the intake manifold through PCV valve
together with the blow-by gas_
At the wide open th rottle, a part of blow-by gas flows into
the air cleaner through the connecting hose of rocker cover on
#1/#3 side and is drawn to the throttle body, because under
this condition, the intake manifold vacuum is not so strong as
to introduce all blow-by gases increasing with engIne speed
directly through the PCV valve.
Under the special operating condition, such as steep right turn
driving, engine oil sometimes blows up into connecting hose or
rocker cover on
#2/#4
side and flows into the intake manifold
by the force of the vacuum.
However, in this case, the connecting hose between intake
duct and connecting hose of rocker cover on
#2/#4
side
reduces the vacuum to prevent th is.
5
®
--~
Fresh air
...... Blow-by gas
- - Mixture of air and blow-by gas
PCV valve
2
pev
hose
3 Blow·by hose (RH)
4
Blow-by hose (LH)
5
Blow-by hose (CTR)
6 I ntake duct
7
Intake manifold
Fig.
3
1800 cc
Valve rocker cover
---.... Fresh air
...... Blow-by gas
- Mixture of air and blow-bY gas
Fig. 4 2700 cc
8 Connector
9 Oil filler cap
10 Rocker cover (#1/#3)
11 Rocker cover (#2/#4)
12 Crankcase
13 Connecting hose
14 Connecting hose
15 Connector
Ll-039
Valve rocker
cover
L2-1257