sorry guys, i was busy and couldnt post reply on the forum.
I took my car to Mini Motors, Cavalry Lahore. Tappets were tight, they adjusted them, plugs were weak, got them changed, wires, according to them, are fine and most important as described by argtr65, the main problem was with stepper motor fitted on the pipe connected with air filter pipe and CNG kit. They told me about this issue. I couldnt notice but they did something with that motor and car worked fine. Normally CNG workshops dont check this motor and they are afraid of touching EFI cars. Any one having similar issue should have this stepper motor checked!
Now from 3 days back, I am again having problem with CNG, it doesnt convert to CNG and engine gets switched off. But after riding it some miles on petrol, CNG works fine. In the morning it takes more miles while afterwards it converts a little quicker.
Everything else is working fine, once converted successfully, pick and milage is good, AC works fine.
What may be the issue? Any expert opinions.
@argtr65 for future problems, what did you do with motor to avoid this issue?