thanks smijaz , xulfiqar , jz for the kind info , surprisingly cng switch and ground connection is perfectly fine now the only thing both cng experts i have consult is faulty fuel pump which wouldnt work when car engine is hot though this theory doesnt make sense to me because car runs on cng when engine is hot while external korean fuel pump remains closed so if its closed it wont make sense it wont work when engine is hot but both of cng experts were convinced that culprit is my external fuel pump and i have to replace it to kabli one or get a geniune intank fuel pump so i guess i have to change the fuel pump soon aswell last but not the least today when engine is reasonably hot and when i was parking my car i tried to convert it cng to petrol and it converts easily so i dont know what is the actual reason behind that , faulty pump , carburator jet setting , or any electrical wiring .