The paper presents results of the experiment focused on evaluation of records of runs of the engine in good condition as a reference for subsequent detection of faults of fuel system of medium speed diesel engine. The aim of research was determination of limits of instantaneous angular speed's spread spotted between random starts of the engine, without any fault condition simulation. Due to fine variation of the load setup and different ambient condition, every record of angular speed of

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... dent starting, despite of attempts to sustain the same load and rotational speed value, presents some deviations between runs. Having on mind utilization of such measurement as a template for further comparison, is crucial to find out how random changes of ambient conditions and accuracy of revolutionary speed setup affect the IAS magnitude course. The answer was got in way of registration of numerous runs of the test engine after independent starts and hand adjustment of required RPM's. The experiment was carried out at laboratory stand in GdyniaMaritimeUniversity, equipped with diesel engine Sulzer 3AL 25/30 driving electrogenerator. Sulzer 3AL 25/30 is three cylinder, medium speed, four stroke marine diesel engine, with maximum output 400 kW at 750 rpm. Independent records were treated as random variable and were compared each other. Obtained results were compared with differences between healthy engine and with simulated malfunctions of fuel injection.