Do I need an EFIE or a MAP Enhancer? 99 Honda Civic

by Dan
(Vancouver Washington)

I have a 1999 Honda Civic DX (D16y7 engine 1.6L), multi-port fuel injection.

Do I need an EFIE to modify the voltage coming from the o2 sensors off the exhaust to the computer, or do I need to modify the voltage coming from the MAP sensor to the computer?

I am confused about when could effectively lean out the mixture to where it should be after installing an HHO system.

Thanks!