In recent years, for an automotive engine, there increases a demand of an environmental correspondence such as an exhaust gas performance and a high mileage, in addition to a demand of a high torque and a high output. For these demands, a CNG or LPG engine is one of the candidates for a low pollution engine. Thus, this paper proposes the high efficiency LPG engine system in which there is no return pass pipe to the fuel tank in the fuel pumping system. That is, by removing the return pass pipe that was considered to be impossible up to now, it is clear that the energy consumed by this return pass pipe is saved. In order to realize this system, the fuel supply by pumping should be precisely controlled so as to meet the fuel just required from the injector of the engine. Since the system is highly nonlinear, a sliding mode controller is used for this control purpose. The effectiveness of the proposed method is verified using simulation and experiments on the real system.