The paper deals with the hydraulic phenomena and the dynamics of individual components of the conventional injection system pump-pipe-injection nozzle. It also describes in detail the influences of individual components upon the fuel injection process. The mathematical model featuring all these phenomena was simulated on the computer. To solve all the equations numerically we applied the Runge-Kutta IV method. The simulation results are compared with the results of extensive and elaborate investigations. The testing of the injection system was performed on a special test stand designed for testing injection systems. The measurements of the effective flow areas were carried out on a test stand specially adapted for testing injection nozzles and pumps. Moreover, the injection systems durability tests were also conducted on special test stands.