Just for future reference - Coil packs and COPs (Coil On Plug) ignition systems are two different animals. The Coil Pack system is what is called a "waste spark" system where the coil pack fires plugs in pairs. (One of the cylinder pairs will be on the compression stroke and its companion cylinder will be on the exhaust stroke - the exhaust stroke spark is useless and therefore refered to as the "waste spark", (but its better than needing a distributor and associtated parts to only fire one plug at a time).

When the coil pack fires, the electrons go out of one coil pack tower, through the sparkplug wire, down the sparkplug core jumping from the plug's center electrode to the ground electrode, travels through the block to the companion plug's ground electrode, jumps the gap to the center electrode, up the sparkplug wire and into the companion coil tower.

(BTW, since one plug fires in the forward direction and the companion plug fires from the ground electrode to the center electrode, thats why you should always use DOUBLE plat sparkplugs.)

In a waste spark ignition system, when a coil pack bites the dust you usually end up with an even number of cylinders misfiring. If only one cylinder is throwing a misfire code it is more than likely a sparkplug or sparkplug wire.

Running with excessively worn sparkplugs with wide gaps strains the coils and causes them to produce excssive heat. Thats why the shop manuals always specify that if you pull a plug wire during diagnosis you should attach it to a ground so that the high voltage doesn't fry the coil windings. So changing plugs helps keep your coils happy.

Same thing with the fuel filter. If you run for mucho miles with a dirty fuel filter it keeps your fuel pump straining against a resistance, causing it to run hotter than necessary. You won't see this pressure resistance up at the fuel rail, but if you look at the pumps current draw with an amp clamp on an osscilloscope you'll see it.