Pull your plugs, check them, if any are compleatly clean or stand out to the rest, put a peice of tape on the wire it goes to, then put them back in

pull them all out, marking them as to which cylinders they go to

unplug wire to coil

run a compleate compression test, any that are low, see which 1's they are, if they are the 1's you had marked with tape because the plugs were washed, more than likely an internal leak

check your oil for antifreeze smell, smell the exhaust

check your thermostat in boiling water to make shure it opens

what color is your smoke, blue, white or black?