i know one is bad but not sure which one ???
how to determine which coil pack is bad. on 1998 Ford F-150
Replace all coils. You will be glad you did, if you plan to keep the truck! Scanner can find misfire, IF you want to replace just one.
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I would strongly recommend a set of eight as well as goo with an OEM or high quality coil. You could try disconnecting them one at a time until you find the one that does not effect how it runs and know that is the failed one as well.