misfire help

99 cobra has a misfire on cyl 8. changed the plug and changed the coil pack
5x already. sometimes when you change the coil pack it will run fine for a day or two then it goes back to missing again. a week ago it threw two codes for misfire cyl 8 and igntion coil malfunction cyl 8. now it throws the check engine light but it says no codes found when you put a code reader to it. im at a loss guys any help would be appreciated.
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Sounds like a frustrating problem. That's odd that the new COP didn't resolve the problem - usually one of those might go bad and a new one solves the problem but you already tried that. :(

Did you clear out the codes or anything by disconnecting the battery ? When did the problem start to appear - after any mods? Do you have a chip or tune/handheld tuner ?

Do you have any aftermarket ignition mods ? : shrug:
no electrical mods. one day it had a back out plug that busted the coil pack so i replaced it. then it started missing real bad. i have been through 3 aftermarket replacements and it would fix it for a day or so then it go to missing again. now im on coil pack number 5 and now the dang thing dont even fire on that coil pack. i unplugged the one coil and the injector to that cyl and the car is still missing.