Terry,

CDI is great for two stroke engines but has fallen out of favour with four stroke engines. The major issue is the risetime of the spark which is around 8-12uS with CDI - great for firing spark plugs that are oiled up. The more usual method is TAI (transistor assisted ignition) where a transistor (FET,IGBT) controls the ignition coil as per my previous post. This has the advantage of less EMI and a longer spark meaning less chance of missfire (less emissions). Much the same as the old Kettering system but the electronics control the dwell (charge time) etc so the coils are optimised for this and give a much 'fatter' spark. As per my previous post, the coil current is either limited by current sense circuitry or the micro knows how long to 'charge' the coil. In cars, my GM DFI (dual fire)system uses current limit circuitry and the micro just controls the firing time, My Kawasaki motorbike doesn't have current limit- the micro does all the work. How do I know this? Because I pulled them apart!! I've learn't most of my techniques by reverse engineering products. I figure that GM( or who ever) since they make 100'000's of these units they probably know a lot more about them than I ever will.