<div class="htmlview paragraph">The paper presents the development of a model study whose results enable to evaluate the torque production non-uniformity between the cylinders of an Internal Combustion Engine (ICE). This non-uniformity can be due, for example, to different air breathing into the cylinders, to different injector characteristics, or to pathological operating conditions such as misfires or misfuels, as well as to other abnormal operating conditions. Between the nominal torque production and the one corresponding to the absence of combustion there exist, in fact, a series of possible intermediate conditions, each of them corresponding to a value of produced torque between the nominal value and the one corresponding to the lack of combustion (due for example to statistical dispersion in manufacturing, or aging in the injection system).</div> <div class="htmlview paragraph">The diagnosis of this type of non-uniformity is a very important issue in today's engine control strategies design. The use of the developed study should in fact allow the control strategy to adopt the appropriate interventions if the diagnosed non-uniformity is for example related to different behavior of the injectors.</div> <div class="htmlview paragraph">In order to evaluate this torque production variability, cylinder by cylinder, information contained in the instantaneous crankshaft speed fluctuations has been processed using a suitable model. The procedure has been validated on an L4 engine in an engine test cell; the in-cylinder pressure signals have been acquired together with the instantaneous engine speed in order to determine the indicated torque produced by each cylinder, and thus evaluate the real cylinder by cylinder torque non-uniformity.</div> <div class="htmlview paragraph">The procedure is able to diagnose abnormal combustions that do not necessarily involve lack of combustion, with the accuracy needed for on-board use. Control interventions to injection and ignition time commands of one or more cylinders should re-establish the torque production uniformity.</div>