at best guess I would say the plugs. Granted Bosch makes some kick ass plugs. But Ford engines (especially ours) are extremely pickey engines when it comes to spark plugs. The best type you should use in these cars is either Autolite Double Platinums(SP?) or Motorcraft plugs. on my Zetec engine I put Champion Double Platniums in which I payed like 20$ for 4 of them. Ran great for about 2 weeks, then my engine cracked one of them and I started to get misfires like crazy. I am back to Misfiring again, but this time its my fuel system, and only if I really horse the engine (im expecting my fuel pump isnt giving much pressure).
