I will present adaptive mesh refinement, special relativistic hydrodynamics simulations of failed GRBs, i.e., jets which are not powered for a time long enough to come out of the star as highly energetic, well collimated GRBs. In particular, by studying the shock breakout, I will determine the fraction of the total energy which is accelerated at relativistic speeds, and compare the results with observations of low-luminosity GRBs. Furthermore, the dynamics of failed GRB will be discussed in detail: the conditions for the jet to escape from the collapsing star will be determined for a broad range of jet parameters and stellar models, as well as the nucleosynthesis resulting by the interaction of the jet with the stellar material.