This paper presents an analysis of the cycle‐by‐cycle combustion variation as reflected in the pressure indicator diagram of a single‐cylinder, naturally aspirated, four‐stroke, direct‐injection, Lister LV1 diesel engine. A measuring set‐up consisting of piezoelectric transducers with charge amplifiers, in the cylinder and the fuel injection pipeline, and a fast data‐acquisition board installed on an IBM‐compatible microcomputer was used to gather the data of 650 successive combustion cycles of the cylinder, under various combinations of injection timing and load conditions. The measured data were corrected for drift, and the top dead centre of each cycle is determined thermodynamically. The data obtained by this technique were analysed for the peak pressure, the peak rate of pressure rise, the crank angles at which these maximum values occur, and for the injection timing and ignition delay. The groups of parameters have been further statistically analysed for averages, standard deviations, probability density functions, autocorrelations and power spectra. Crosscorrelation runs were also performed to observe any cause relationship between cyclic pressure variations and the fuel‐injection‐system operation. The results of the stochastic analysis technique have proved to be very useful for the investigation and interpretation of the existence of fluctuation phenomena in the diesel internal combustion engine and their cause relationships, thereby aiding the correct interpretation of the relevant experimental results and their associated errors.