@Rozzz
there is no worn with coils..M series engine have been used worl wide..and running on very hig setup as well
world wide these cars arnt being used on CNG 
@caridnal, its not Suzuki Pakistan thats using this, waste spark system is being used in many cars world over, Santro has it, Lancer 1.3L has it.
But the issue remains. while bloging, searching and googling i came to know Iridium plugs solves the problem.
The reason for misfirning is that on petrol a car generates about 12 volts, while on CNG it makes about 8 volts, the current isnt sufficient enuff to travel to the dependent cylinder. due to which it misfires.