The paper presents the methodology and tests results of the influence of the fuel injection pressure and combustion chamber back pressure on the changes of the fuel spray geometrical parameters injection uniformity and its quality during the injection. While evaluating the geometrical fuel spray parameters the spray penetration, speed of propagation were taken into account and while evaluating the quality of the fuel atomization the outflow of the fuel from the injector were considered. The tests reported here were performed for one value of the air back pressure at the various injection pressures. The fuel doses were changed by modifying the duration of the injection. A significant influence of theses parameters on the values of the operating indexes of the injection and atomization processes has been noted.