Adding a vaporiser, getting the computer to run right.
Ok say you have a reasonable vaporiser. Ie it completely vaporises enough fuel to cruise on the highway at 100km/h. So you have just discovered a bolt-on way to improve economy a lot (I just had a brainwave on that, but I'll tell you in the induction section), but the standard computer cracks up, and decides that no matter what you say or do, it won't remove enough fuel down low for your invention to be any real benifit.
So what can I do about this? Due to the nature of said invention, fuel flow is pretty limited, so running it as the only fuel supply isn't an option.