closetguy,

Just for the heck of it, with the Taurus, did you ever try attaching the ignition ground strap directly to the head instead of a mounting lug or strapping it to the spark plug? By drilling a small hole in the top cooling fin of the head and attaching the ground there you just developed the best gound you can get on the engine. It ALWAYS works. The mounting lugs on the engine are often a poor ground for some reason, and clamps always loosen.