<p>A modification to the gas-topping invention disclosed in WO 2008/064415 is disclosed in this specification. The modification involves measuring a sensor input such as that provided by a diesel engine diesel fuel rail pressure sensor (5) to thereby provide a signal indicative of fuel flow rate, modifying that signal by a signal modifier (3), and substituting the modified signal for the original unmodified signal in an engine electronic control unit (7). The result is that there is no increase in engine power relative to that produced without gas-topping so that substantially all the benefits of gas-topping are captured in decreased fuel consumption and not to provided in the form of increased engine power.</p>
