| The reason a standalone ECU is needed is because the OE CAS has 360 trigger points in its wheel and the OE ECU expects to see this many trigger points to process properly. I don't know the reason for the OE system being built around so many trigger points, but no matter how many, it's still driven by the cam with a not-so-direct link (timing belt) to the crank. And this system results in what is known as "timing scatter" which plagues all 4-stroke engines with ignition systems driven by a camshaft. It is easily viewed with a timing light at idle and all ignition timing trims set to zero. The problem with timing scatter is that it has a plus and minus effect on the target number because the timing belt stretches and contracts and the cams can decelerate during valve opening and accelerate during valve closing events. Subtracting some timing will just reduce the power a bit, but if the scatter adds some timing at full load and it's enough to cause the fuel to detonate, nothing good will ever come from that. In a nutshell, the crank trigger is much more precise ignition system than the cam-driven CAS.
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