Crankcase Ventilation Systems: Operation: Notes

During part throttle engine operation, intake vacuum pulls the blow-by gases through the PCV valve. The capacity of the valve is sufficient to handle the blow-by plus some of the ventilating air. Ventilating air is drawn from the carburetor air cleaner, or through the throttle chamber on 280ZX and 810 models, then through the tube connection and into the crankcase. Under full throttle operation, the manifold vacuum is not sufficient to draw the blow-by through the valve. These gases then go through the tube to the air cleaner in a reverse direction. Engines with excessive blow-by will pass crankcase vapors through the tube to the carburetor during all conditions.