>4,500 rpm problem.

HISSIN50 said:

With some cars, especially if the ignition is a bit aged or there are mods to the car, plats can cause a low idle and a misfire around 4K RPM. Plat doesn't conduct as well as copper (i.e., Autolite 25's for E7 heads). When a higher RPM misfire pops up and plats are run, it's one of the first places I look. Since plats don't perform as well as copper (but last much longer - the lack of conductivity is made up for with low gap erosion), swapping in some coppers is something I don't hesitate to do.

There are more than a few folks that run plats without issue. You're lucky in that you're one of them. There are also a lot of folks that had issues from running plats.

Jeff, as 95Cobra302 said, a fox III coil will work. So will a lot of the coils from other EEC-IV Fords. Since you had the issue with two different coils (from the sound of it), you probably don't need to worry about your coil.

Because the issue is intermittant and sporadic, I think some fresh copper plugs might do the trick for you. I'm really just guessing though bud. Also let us know what your plug gap was at. If much over stock spec and the plugs are plat, that could be it (you cannot really re-gap plat plugs, so you're stuck with them as they come out of the box).

Though stock is 0.052-0.056", I start my coppers between 0.045 and 0.050" to allow for some gap erosion (unless you check or swap plugs often, where you won't ever have much erosion).

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