[shorod]

If the 1999 is like the 2000 (which I suspect it is) there are two coil packs on the V8. I'm not sure I'd say it is normal for a pack to fail, but it is not uncommon for coils and coil packs to fail in general. It's not a Ford issue on these.

Has your dad pulled codes for the Mountaineer that shows a misfire code on the 2 cylinders? Do they happen to be 2 cylinders that share a coil? The two packs are the same part number, so you could swap them out and see if the misfire codes follow the coils.

Did the issue get any better or worse with the new plugs and wires? I did experience an intermittant MAF sensor on my 2000 Mountaineer V8 last winter that would cause a random loss of power which sometimes felt like a misfire. On the highway, it felt more like a very short complete loss of power. Fortunately the PCM was smart enough to detect the intermittant MAF and set a pending code for an intermittant MAF sensor. Ford hasn't had MAF sensor issues like GM did in the '80's and '90's though, so I wouldn't shotgun out the MAF if there isn't a code for it.

-Rod