i have chevy joy 2006 cng is not genuine my problem is while driving on cng car goes to petrol automatically and it comes back after 3-5 seconds with a big jerk,mechinics says it is cng wiring problem like earth(grounding) problem but they are unable to figure it out.also while running on cng with A/c on car start doing missing and jerking in low gears and no pickup then i have to turn off a/c and everything goes fine instanly.\plz give me some suggestion.i tune up my cng 3-4 times and also cleaning of plug but my problem remains.