Abstract: Control apparatus has a double-acting hydraulic cylinder and a piston reciprocable in the cylinder in response to application of suitable hydraulic pressures to the piston. The ends of the cylinder are connected to a source of hydraulic pressure by means of two-position valves. The piston is connected to one rod and the cylinder to another rod -- the two rods forming part of a linkage between a gas pedal and a fuel injection pump. An electronic apparatus controls the valves to change the overall length between the outer ends of the rods to change the effective length of the linkage and to control the fuel injection pump.