Abstract: In an internal combustion engine employing intermittent, pulse-controlled fuel injection, the amount of fuel, i.e. the duration of the control pulses is made dependent at least on engine speed and the degree of opening of the throttle plate. These variables are converted to electrical signals which are used to generate an approximation of the optimum pulse duration values as a succession of linear approximations added to an initial value. The throttle angle signal is fed into an amplifier that limits the output signal above a certain value of throttle opening, e.g. 50.degree.. The speed signal feeds into a ramp generator and the throttle signal controls an initial value generator. The outputs from these generators are summed and compared with a maximum value and at least one minimum selector selects the lower of these values for use as the injection control signal.