Installed a Ford 5.4 mod motor in a fox body. Motor was running strong, after last tune-up. Started it up one morning and drove about 5mi, shut it off for about 3min. When I started it up again it had a bad miss. I installed steel inserts to stop the the spark plug blow-out, new plugs, and coils. I did notice that one plug was fouled real bad and the cylinder didn't seem to hold pressure to well.. Need help, Thanx.......