The compressed combustion gas which escapes past the piston rings into the crankcase is known as blow-by gas. Blow-by gas contains large amounts of CO and HC. The positive crankcase ventilation (PCV)system prevents the blow-by gas from being emitted into the atmosphere. The PCV system routes the crankcase blow-by gas back into the intake system where the blow-by gas becomes part of the combustion process. The PCV system consists of the following components:
The primary control of engine crankcase blow-by gas is the PCV valve. The PCV valve meters the flow of blow-by gas according to the manifold vacuum signal.
In order to maintain idle quality, the PCV valve restricts the flow of blow-by gas whenever the intake manifold vacuum is high. Abnormally high crankcase pressure may cause the blow-by gases to flow through the crankcase vent tube and into the air cleaner. The blow-by gases are then drawn into the intake system and consumed in the normal combustion process. The relationship between the flow of blow-by gas and the engine manifold vacuum is charted in the following table:
Manifold Vacuum
PCV Valve Opening
Blow-by Gas Flow
Low
Large
High
Small
A plugged valve or hose may cause any of the following conditions:
A leaking valve or hose may cause any of the following conditions:
