Actauly the EFI car needs a ECU to control so thats y its still in working. (you have to install a emulator to give false readings remember) secondly chalne ko her gari chalti hai no issues.
The things i was reffering to.
Vitz has smaller valves,
Vitzes brakes get harder on CNG (sometimes people have complained there not able to brake the car).
Normal gari mei (aye din battery down)
Har hafte air filter ka jhanjhat.
Shorter oil drainage periods.
If u dont drive on petrol (most CNG car owners jst start the car on petrol and think its enuff) fuel filer, fuel pump, petrol injectors Die pre maturly.
short ignition coils. (common in Efi cars, noticable only in Liana, Baleno nd Lancer nd Santro because in those cars one coil is responsible to 2 cylinders while in other cars if one coil is short you only feel minor missing 4 seperate coils for each cylinder.) and you know wat all the above costs for a EFi car rather then a Carby cultus, alto, mehran, coure. 
CNG is okay wid those people who fully avail it, i.e who have atleast a 60 to 80 kms running a day. Normal cars wid home running are driven for grocery in gali mohalla wid full time a.c on only make upto 80 to 100kms Maximum (i can chalenge it/ or mayb my driving habbits differ) in full 55kg (fills in around 450 to 500) cylinder.
Itna to meri vitz 500 k petrol pe chaljati hai (90 kms on Rs 500 Petrol).
