First thing would be to check all the wires then check all the plugs (Check for cracks in the porcelain). If those are good I would take two wires off the coil pack (that are next to each other) at a time and crank it over to see if it arcs between the two terminals on the coil pack to see if that is good. If you still can't find an issue I would keep going with the stuff above and possibly more.