The compressed combustion gas which escapes past the piston rings into the crankcase is known as blowby gas. Blowby gas contains large amounts of carbon monoxide (CO) and hydrocarbon (HC). The positive crankcase ventilation (PCV) system prevents the blowby gas from being emitted into the atmosphere. The PCV system routes crankcase blowby gas back into the intake system where it becomes part of the combustion process. The PCV system consists of the following components:
The primary control of engine crankcase blowby gas is the PCV valve. The PCV valve meters the flow of blowby gas according to the manifold vacuum signal.
In order to maintain idle quality, the PCV valve restricts the flow of blowby gas whenever intake manifold vacuum is high. Abnormally high crankcase pressure may cause the blowby gases to flow through the crankcase vent tube and into the air cleaner. The blowby gases are then drawn into the intake system and consumed in the normal combustion process. The relationship between the flow of blowby gas and engine manifold vacuum is charted in the following table:
Manifold Vacuum
PCV Valve Opening
Blowby 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:
