With the aim of developing advanced injection strategies to linearize as much as possible the injected mass diagram, we decided, as a first step, to study and model the complex dynamics of a solenoid fuel injector: this paper hence deals with the realization of a mathematical model for the prediction of both the needle motion and the injected mass of a gaseous fuel injector, with particular reference to the nonlinearities of the injector flow chart. The model has been realized with a zerodimensional approach and supposing the injector to work in choked flow condition (which is usual for gaseous fuel injector). Moreover, to lower as much as possible the number of parameters to fix by model identification, a strong grouping work has been done, introducing some dimensionless groups. This allowed us to reduce to only seven the constants to fix by calibration, which was performed by comparing the model output results with experimental data acquired on the test bench. Although a simple zero-dimensional approach has been followed, the model revealed good reliability since not only reproduced quite well the nonlinearities of the real injector flow chart, but proved to predict with unexpected accuracy also the injected mass and the solenoid current related to air pressure cases different from the calibration set. The model prediction error, in terms of injected mass, was found to be of the same order of magnitude of the experimental uncertainties.