How do you know when a coil pack has gone bad? I'm getting misfires deteced by the computer in #1 and #3, so I was going to start wiht plugs since the ones in there are original and have 70k miles on them. Should I buy a couple coil packs too? 2002 3.0.

 

Misfires are usually the coilpacks. You can move the coilpacks to the other cylinders and see if the misfires follow