Using an elastic model of the engine -drivetrain system, measured speed fluctuation data is passed back through the model to determine the fluctuation waveform of both the total engine torque being developed and the engine pressure torque. The torque fluctuation waveforms are available on a cylinder by cylinder basis. Utilizing the engine pressure torque fluctuation waveform, the mean level of engine torque being developed is obtained, thus providing the full engine pressure torque waveform. Finally, the engine pressure torque waveform is used to obtain the cylinder pressure waveform which gave rise to it. Knowledge of these torques and of the cylinder pressure provides the basis for both open loop and adaptive engine control strategies.