An injection molding system comprised of: an injection machine having a barrel and a screw for injecting an injection fluid, a distribution manifold, a valve associated with a corresponding one of one or more downstream gates, a sensor adapted to sense and generate a signal indicative of pressure of the injection fluid in the barrel or an inlet that delivers injection fluid from the barrel to the manifold, and a controller receiving the signal generated from the sensor and including instructions that use the signal as a control value to adjust, during the course of an injection cycle, positioning or velocity of one or more of the valve pins.