I think it goes back to the previous step, if you don't have all "juice" in on the primary winding in the coil...you don't get all juice out from the secondary winding to the spark plugs.
I would still look for the reason why you have that low 11.something volts in to ballast resistor and corresponding low voltage (= low current = low energy = weak spark) to the coil.


Martin, 67 Charger, 512 cui, E85, MegaSquirt MS3X sequential ignition & injection