Crankcase Ventilation System Description

Crankcase Ventilation System Description
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 PCV valve
- The crankcase vent or air inlet tube
- The air inlet filter or separator, if used
- Any hoses or couplers

Operation
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.

PCV Valve








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 table.

Results Of Incorrect Operation
A plugged valve or hose may cause any of the following conditions:
- A rough engine idle
- Engine stalling or low engine idle speed
- High engine crankcase pressure
- Engine oil leaks
- Engine oil in the air cleaner
- Oil sludge in the engine
- Engine oil consumption
- Excessive exhaust emissions
A leaking valve or hose may cause any of the following conditions:
- A rough engine idle
- Engine stalling
- High engine idle speed
- Incorrect engine crankcase pressure
- Excessive exhaust emissions