Positive Crankcase Ventilation: Description and Operation

GENERAL DESCRIPTION
Blowby Gas
"Blowby gas" is the compressed gas and exploded gas which passes by the piston into the crankcase. Blowby gas contains a large amount of unburned HC gases and partially burned gases such as CO and HC. The Positive Crankcase Ventilation ([1][2]PCV) system is provided to prevent the blowby gas from being emitted into the atmosphere.

Metered Orifice Type
The PCV system is a metered orifice type which supplies vacuum from the intake plenum through a vacuum hose to a metered orifice in the valve cover. The PCV system draws out blow-by gases at a controlled rate.

SYSTEM COMPONENTS
The PCV system consists of a [1][2]PCV hose and metered orifice mounted in a valve cover.

OPERATION
The PCV system draws out blow-by gas through the metered orifice, through the [1][2]PCV hose and into the intake plenum and is consumed by normal combustion.


RESULTS OF INCORRECT OPERATION
A plugged metered orifice or hose may cause:
^ rough idle
^ stalling or slow idle speed
^ oil leaks
^ oil in air cleaner
^ sludge in engine

A leaking metered orifice or hose would cause:
^ rough idle
^ stalling
^ high idle speed