Crankcase Emission Con - Subaru 2002 Impreza Service Manual

CRANKCASE EMISSION CONTROL SYSTEM
Emission Control
(Aux.
Emission Control Devices)
3. Crankcase Emission Control System
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The positive crankcase ventilation (PCV) system prevents 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 fresh air inlet, connecting hoses,
a PCV valve and an air intake duct.
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In a part-throttle condition, the blow-by gas in the crankcase flows into the intake manifold
through the connecting hose of crankcase and PCV valve by the strong vacuum created in the
intake manifold. Under this condition, fresh air is introduced into the crankcase through the con-
necting hose of the rocker cover.
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In a wide-open-throttle condition, a part of blow-by gas flows into the air intake duct through the
connecting hose and is drawn into the throttle chamber, because under this is condition, the intake
manifold vacuum is not strong enough to introduce through the PCV valve all blow-by gases that
increase in the amount with engine speed.
EC-6