my santro executive gives backfire in slow and takes jerks. i consulted with CNG expert and he advised to change its EFI advancer (Zentec) which was not functioning. meanwhile the plugs/ plug leads are also being checked. After replacing advancer with new one (PVR) the problem is still there. Also the car consumption is very much. it gives only 70kms in 40 kg cylinder. plz any body expert opinion.