Gasoline Models

During part throttle engine operation, intake vacuum pulls blow-by gases through PCV valve. Capacity of valve is sufficient to handle blow-by plus some ventilating air. Ventilating air is drawn from carburetor air cleaner, or through throttle chamber on Maxima and 280ZX models, then through tube connection and into crankcase.

Under full throttle operation, manifold vacuum is not sufficient to draw blow-by through valve. These gases then go through tube to air cleaner in a reverse direction. Engines with excessive blow-by will pass crankcase vapors through tube to carburetor during all conditions.