Abstract: An improved method and apparatus is provided to control the rate at which fuel is supplied to an engine by a fuel pump. The fuel pump has an output pressure which varies with pump operating speed in accordance with different curves of a series of curves. In order to determine which curve of the series of curves is representative of the manner in which the fuel pump output varies with pump speed at one time, the fuel pump operating speed and output pressure are simultaneously sensed to determine a point on an initial curve. The fuel pump operating speed is subsequently varied in accordance with the initial curve to provide a desired variation in fuel pump output to the engine. The fuel pump operating speed and output pressure are periodically simultaneously sensed to determine if the fuel pump output still varies in accordance with the initial curve or has changed to a second curve of the series of curves.