Fuel system

A fuel injection system for an internal combustion engine comprising a plurality of pump/injectors actuable by engine driven cams, the pump/injectors delivering fuel to the combustion chambers of the engine respectively, each pump/injector comprising a housing in which is defined a bore, a reciprocable plunger in the bore, the plunger being movable inwardly in the bore by a respective engine cam, the plunger and bore defining a pumping chamber from which fuel is expelled during inward movement of the plunger, a fuel injection nozzle mounted on the housing, the nozzle having an inwardly opening valve member which is biased by a spring to a closed position and is movable to an open position to allow fuel flow to the engine by fuel under pressure supplied from the pumping chamber, the spring being housed in a spring chamber the fuel pressure in which acts to assist the action of the spring, an electromagnetically operable spill valve having a pair of ports which are connected together when the spill valve is open, one of said ports communicating with the pumping chamber and the other of said ports communicating with the spring chamber, means restricting the flow of fuel from the spring chamber, and a first non-return valve interposed between said other port of the spill valve and the spring chamber, the restricting means of each pump injector being interposed between the spring chamber and a common passage and pressure control valve means for controlling the pressure in said common passage.