Hello; Answering your first question of the high voltage by the voltage regulator will be the first thing to check. But it is necessary to take into account that one of the causes that often affects the life of the coil (s) is the resistive state of the spark plug wires and I explain why, the coil generates a certain amount (flow) of high voltage at each pulse, if this flow rate is not evacuated freely in the circuit consisting of wires and spark plugs, a high voltage build-up occurs within the coil raising the temperature of the coil by burning the internal insulation between threads. As a daily example I tell you that, it is like when you squeeze the tip of an irrigation hose, you decrease the flow rate and increase the internal pressure in the system With which you must measure that in the cables there is no more than 8 Kohms per linear meter, in a cable of 0.50 cm. you can't measure more than 4 Kohms, right? Except in cases, which I don't think is yours, there are cables whose resistor is carbon based and can double the resistance, but if you have the originals with inductive reactance, take into account the first definition. For spark plugs you should measure a value of 1 to 2 Kohms, however with the problem you have I recommend, unless you have already done so, replace both games. As for your last question about the ECU output pulse, it is a possibility, but much more remote than before, there were cases in which the drivers did not work sufficiently grounded increasing the temperature of the coil.