Abstract: A device, and associated methods, for converting a fuel-injection engine, originally intended for use with a first fuel, allow the engine to operate with a different, second fuel (e.g., bioethanol, alone or mixed with unleaded fuel(s)). The device delivers an adapted injection signal to an injector based on an original injection signal (SI) received from an engine control unit. An analyzing, circuit includes a measuring circuit, to measure the SI; a detecting circuit, to detect an end time of the SI when the measured signal drops below an end threshold; and an updating circuit, to update a value of the end threshold, depending on the measured signal. A signal generator produces a complementary injection signal (SC) starting from the end time. A switching circuit transmits the SI to the injector, then delivers the SC to the injector. The SI and the SC together form the adapted injection signal.