A locomotive propulsion system includes an engine assisting apparatus and an engine control unit that monitors an output parameter of a locomotive engine. The control unit determines whether the engine output decreases sufficiently low to at least partially de-fuel the engine and to activate an assisting apparatus. This assisting apparatus rotates a shaft of the engine with or without the engine also rotating the shaft. Rotation of the shaft by the assisting apparatus can be used to power traction motors or other loads of the locomotive while reducing fuel consumption and/or emission generation by the engine.