basically the coil is where the power is amplified/stored/released and the ECU is pretty much just an on/off switch for the primary current that is the input for that power tho a box (ECU) has to be capable of switching however much pri current the coil is using and not electronically delay that switching which in effect retards the timing which is the "pulled timing" complaint that you hear (sometimes) on orange boxes (plus em dieing!), the newer ones that is. I cannot ans your Q, just bored on a Sat night