The invention utilizes the firing order of the cylinders within the engine to identify the cylinder or cylinders that mainly contribute or, alternatively, contribute as little as possible to the production of certain harmonic frequencies in the engine's torque. In order to use the engine's torque for this purpose, the calculation of torque must take into account the non-linearities of the engine system. Thus the calculation of torque takes into account not only the properties of the engine but also the properties of the load and the shaft.