Bad Coil again??

Hi,
I have a 98 Navigator with 110k miles. Last January I had the no. 3 and 8 coil replace (check engine). The car ran like crap...so that fixed it. Eight months later it did the same thing, so I had the remaining 6 coils replaced.... so that fixed it. A week ago the no. 3 went again, I took it back to the mechanic and he replaced it. A couple of days later check engine came on again and now its running worst than ever before. When its on idle and when I accelerate it misses. Its like I'm driving a 3 cylinder car. I can't keep replacing these coils as they are not cheap. Obviously something else is making them go bad, but what is it, I don't know. Pls. help.

Oh and Happy Thanksgiving!

You Might Wanna Try Replacing The Plug Wires. Sounds Silly, But I Had A Friend Who's 99 Expedition Would Mis All The Time. He Changed The Plug Wires And All Was Good.

You must have the 5.4L engine with a coil for each plug. Are you using the double platinum plug which is properly gapped. I would just replace the defective coil. Do you have any gas or water getting on them. I would have him check the ground wire for them to be certain it is tight. I would also check the relay to be certain full current is flowing through it. You use a temp wire and energise it and use an ohm meter to check for continuity on the other prongs. Low voltage will damage a coil.