Abstract Changing of some engine structure parameters affects the emission of harmful components in the exhaust. This applies mainly to damages occurring in the charge exchange system as well as in the fuel system and the engine supercharging system. Changes in emission of harmful compounds are often ambiguous, because they depend to a large extent on the parameters that shape the combustion process. An additional problem is that often simple interactions occur with the interaction of these parameters. It is, therefore, possible to speak about different sensitivity of diagnostic parameters to the same extortion from the engine structure, but implemented in different load states. In the paper, the authors propose a methodology for the classification of acquired diagnostic parameters using the Hellwig’s information capacity indicator method, which is the basis for building a ranking of diagnostic parameters based on the zero unitarisation method. At the same time, the diagnostic model of the engine will be presented, based on the theory of multi-equation models, in which the diagnostic symptoms are indicators and characteristics of the emission of gaseous exhaust components. The research confirmed the existence of a strictly defined relationship between the structure parameters of the studied engine systems and the toxic emission factors. All the features of the initial parameter were also positively confirmed as a diagnostic parameter, i.e.: unambiguity, sensitivity and availability. This allowed for an optimal selection of engine work areas in which the response dynamics (sensitivity) of the adopted parameters is the greatest. The research methodology used allows for the formulation of general conclusions and thus the wider application of collected empirical material.