I have 98 1.6 Zetec escort and it miss fires and runs on 3 cylinders at times. I have changed the plugs, and its fine for a while, when I take the plugs out the ceramic has got thin cracks in it and you can see where the spark has been tracking acrossed it. I have changed the leads. thinking of changing the ignition unit that the HT leads come out of. Any ideas please. Driving me MAD