How is your primary voltage doing? If you connect oscilloscope to the ignition coils primary contacts the voltage should be 12v with ignition on, during starting the signal should be rectangular. If you can see this then your ignition module is fine.
If i understand correctly you have a conventional ignition system ( you have a coil and high-voltage distributor).
Even if you will not get the rectangular signal, first of all the voltage supply of ignition module and the signal from engine speed sensor should be checked.
I think you should replace the ignition coils on trial basis(but you have to use the brand new ones).
I had a similar problem with 4.2 Sklasse. engine would not start.
I cleaned the spark plugs with gas burner and the engine would start immideately and i advice you to do the same thing. After cleaning of the spark plugs engine worked fine for couple of days and then the problem started again. Problem was solved by replacing the ignition coils. So try to either clean or replace the spak plugs and let me know the result.