The fuel supply system of an internal combustion engine delivers liquid fuel to electrically operated fuel injectors by means of an electric pump whose output pressure is regulated by control electronics which receives as feedback from a pressure sensor connected into a fuel delivery passage serving the injectors a signal representing the pressure differential between manifold absolute pressure (MAP) and absolute pumped fuel pressure. The pressure sensor has a movable wall that divides its interior into an intake manifold pressure sensing chamber space communicated to the engine intake manifold and a fuel pressure sensing chamber space communicated to the fuel delivery line to the injectors. A magnet is mounted on a central region of the movable wall to transmit a signal to a Hall-effect sensor mounted within the intake manifold pressure sensing chamber space. The feedback pressure signal is derived from the Hall-effect sensor sensing the position of the magnet, and hence that of the movable wall.