A fuel economy method and system consists of using a signal control unit connected to a throttle of a vehicle and to a mass sensor for sensing a mass of a load carried by the vehicle. When the sensor senses that the mass is within a predetermined mass range below a pre-determined load mass value, the signal control unit reduces the range of power output of the engine. The unmodified engine power output range and modified engine power output range extend from a minimum engine power output to, respectively, an unmodified maximum engine power output and to a modified maximum engine power output lower than the unmodified engine power output and thereby requiring less fuel. Accordingly, the range of engine power output, and notably the maximum engine power output available, is reduced when the mass is in the pre-determined mass range, thus reducing fuel consumption compared to the unmodified engine power output range.