I recently researched specs for the ignition coils for a 97 F150 4.6l and found that in the Autozone manual they give two test criteria for resistance. The primary test taken from the three prongs where the wire connects has a range of .3-.7 ohms. The secondary test which is taken at the point where the spark plug wire connects has a range of 11.11-16.6 ohms. I checked a new coil while at Autozone and got readings of .8 ohms on the primary and 11.2 ohms at the secondary. The coils on my truck have readings of .9 ohms and 14.4 ohms respectively. I do not have a Ford manual to confirm the specs and was hoping one of you had one. My truck was missing badly so I replaced the wires and she ran good for a day or two then started missing again. Got a misfire code on # 4 so I replaced the plug(only 25k miles on it) and shes running good again. I have read where bad coils might make the wires and/or the plugs go bad.
I read where you had valve problems so I checked the compression and no problems yet. The plug looked perfect, the gap was still right on. Normally with a burn't valve you will get a puff of that ugly blue smoke right when you crank her over.