Abstract: An engine control system is disclosed wherein torque or slip speed of a fluid coupling or torque converter is used for the control of an engine operating parameter, such as ignition spark advance. In the fluid coupling or torque converter, the respective speeds of the impeller and turbine are sensed by sensors which respond to the passing of each blade of the respective impeller and turbine. The speed signals are applied to computing means to produce a control signal corresponding to either slip speed or engine output torque, as desired, according to a predetermined functional relationship of the speed signals. The control signal is applied to control means which is operative to adjust a selected engine operating parameter. In a particular embodiment, the control means includes detecting means for determining changes in the value of the control signal and also includes a controller for the ignition spark advance which advances or retards the ignition in order to optimize the engine output torque.