Fuel injection systems

A fuel injection system comprising a pumping plunger slidable within a cylinder, actuating an outlet from the cylinder and a non-return valve in said outlet, means for effecting movement of the pumping plunger in a direction to displace fuel from the cylinder through said outlet, a fuel inlet to the cylinder and through which fuel can flow into the cylinder during the return motion of the pumping plunger as permitted by movement of said actuating means, a non-return valve in said inlet, valve means defined by the plunger and actuating means, said valve means being maintained closed during movement of the pumping plunger by the actuating means, and the system including a stop to limit the movement of the actuating means whereby in use, the pumping plunger will continue to move after the movement of the actuating means has been halted, so that the valve means will open to cause a reduction in the fuel pressure in said cylinder.