Toy used as inexpensive a transistor that could form a reliable ignitor. Use a larger power transistor (a bit more expensive0 and redesign the ignitor or copy a design from some library that could be found on google. Measure the ecu signal coming to the ignitor with your scope and the ecu output and ignitor input. Make a better thermal dissipating hardware setup to keep the transistor cool. This is ancient, ancient art and easily solvable without looking at the contents of the present ignitor if you want to spend the time and if you have a discrete transistor/FET design background.