The aim of this study is to present a mathematical model for the wave pressure in the Diesel injection system. The method of characteristics and the finite difference method have been used to solve the governing equations. Recent studies show that finite difference method is superior to the method of characteristics concerning computation time and nonlinearity. The injection process of a high-speed Diesel engine was studied in detail, using an original computer program developed in MATLAB. The governing equations are solved by the use of the finite difference method with central pattern at space coordinate in combination with the separation of flux vector. The fuel injection system is divided into pump, pipe and nozzle component to model the entire system. When forming equations of continuity and motion the following assumptions are considered: all the equations have 1D spatial resolution, temperature change due to pressure and time during the cycle is not considered, the vapors pressure of the fuel is small compared to the level of the pressure injection system, it is assumed that cavitation will not occur and elastic deformation in the injection system is not considered. The experiment is carried out to measure the fuel consumption, in-cylinder pressure, the fuel injection pipe pressure near the injection valve and needle lift for several regimes of the working domain of a Diesel engine. The experimental set-up includes a 4 stroke cycle 4 cylinder Diesel engine T684 made by Tractorul Brasov Romania. Simulations show satisfactory results, in principal for regime of low speed, for regime of high speed it is important to take into account cavitation and the elasticity of the component; but improvements are possible. Since the models are developed for certain conditions it was not expected to be valid for all working conditions. Targets for further research related to the present work is to improve the model attaching submodels for cavitation and elasticity of the component