Mitsubishi Montero on 1996 System Problem

The truck starts, but does not work a coil that generates the spark for cylinders 3 and 6. I am interested in knowing the causes that could generate this type of problem. In advance, thank you very much for the support.

The first thing Czech the coil by changing it for another for example 1-4 and tests if the same cylinder fails, if then cables and spark plugs and by last Czechs the signal if the coil is successful depending on that is what will have to be proven and do about it, but that to eat has the face of being a coil and nothing else.