Fuel air mixture is an insulator - the more that you cram into the cylinder the higher the resistance. At some point a coil that can jump a gap at part throttle will start to have trouble with the higher peak pressures of full throttle running. With a powerful enough coil you can run wider gaps, but there isn't much a a noticeable difference in the way it runs. I kept the OEM plugs in my new Jetta until around 130K miles - when I took them out the ground electrode was eroded *way* back for a massive gap - and it still ran flawlessly with that uber-powerful coil pack zapping them.

I'm not sure what is happening with your car. One thing that comes to mind is a failed diode on the alternator. The alternator produces (as the name implies) alternating current when it spins. Not of much use in a DC car electrical system, of course. So they use a heavy duty diode which only allows current to flow one way and use that to rectify the AC current into a chopped DC flow. If the diodes fail and allow current to flow both ways, the alternaotr will not charge anymore, and can allow electricity to flow "backwards" though the alternator. Diodes can be damaged through when charging a car - most usually when someone hooks the cables up backwards - or if you hook a battery up backwards. The diodes can handle the current flow produced by the alternator, but greater loads produced by fast chargers or a backwards battery can burn them out.
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I'm JohnMc, and I approved this message.