Glenn, I suspect you have a plug wire that's open or nearly so. Our Explorers use a "lost spark" system in which one bank of cylinders serves as a ground circuit for the coil pack. (Each coil fires 2 cylinders, on both the exhaust and intake strokes). An open or very high resistance wire might be causing the coil to overheat.

I'd check each wire with an ohmmeter, and look for the one with high resistance or showing an open. Replace it and the coil pack, and drive it back home.

There's an outside chance the resistor is burnt open inside one of the plugs, which would give the same open condition. Bottom line is new wires and new plugs are in order (and another new coil pack).....Resistance values are about 5K ohms for a plug, and up to about 10K ohms per foot of wire.