Impreza 2.5 RS Sedan AWD F4-2.5L SOHC (2002)
Positive Crankcase Ventilation: Description and Operation
Crankcase Emission Control System
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 connecting
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.
