HHO Hydrogen Dry Cell Car Conversion?

I have installed a homemade dry cell of 11 plates, with 5.5 amps at 13.5 volts.
It has given me an increase in mileage with CNG of about 5% by reducing CNG feeding and putting a tape to reduce air. I want to know what can be the solution for EFI cars with out EFIE? Does the EFI system in EFI cars work with CNG? If not then why am I getting poor milage with CNG with hho. The amps of my hho dry cell goes down to 0.5 A from 5.5 amps. Why?