Abstract. This paper concerns measurement and modeling of cylinder pressure in diesel engines. The aim of this paper is to build the empirical-analytical model of engine working cycle. The experiments on engine test bench were conducted. The new genetic-fuzzy system GFSm was proposed. By means of GFSm, the engine working cycle model was built. This model allows simulation of cylinder pressure for each allowable crankshaft speed, and loads and also for several biofuels. The model can be used to evaluate the quality of working cycles of piston engine with an accuracy required in practical technical applications.