Blinking engine light, rough running, smells like gas from exhaust on Ford F 250 Super Duty?

For gas engine.

the blinking light is blinking a code that ID's the cylinder or cylinders that is mis firing, count the blinks, poss causes are defective ignition coil (one for each cylinder) or a defective spark plug, these are the common reasons other problems of course like a dead cylinder from low compression like a bent or burnt valve can also cause this, but that is very unlikely.