Did the trick on my old Pontiac that had a very sick ignition system. I think my biggest problem was a cracked Ignition Coil Covering along with perhaps a bad Ignition Coil. However no ace mechanic, so I just replaced the whole ignition system with ACDelco original parts. I read all over the internet that ACDelco original parts were an absolute necessity for my very finicky old car. Whatever, it now runs great with these spark plugs when it had been a low powered back firing sputtering mess before I fixed it.