[AJT1961]

This happened to me once. Turned out the problem was that there was a hairline crack in one of the brand new AC Delco plugs which I didn't notice which caused the plug to ground out. I still have a few gray hairs from the day it took me to figure that one out. Also, it could be a bad ignition wire made worse by the handling necessary to change plugs. Or as old master mentioned, it could be a crossed wire -- it's easier to do that than you'd think if you don't follow the "one at a time" rule -- but on the bright side, you usually only make that mistake once in your lifetime.