Aaron -
welcome to the board. There is a lot of good information here and the members are very knowledgeable and helpful.
the other mods (efie, map, maf) are designed to fool the car's ECU into running leaner (to make up for the added O2 in the exhaust stream from the HHO burning) by making the ECU run lean, this is how we achieve MPG gains.
Some vehicles do not require mods while others do. Your setup may vary. I would get a baseline MPG to start with based on miles driven per fillup. Then add HHO and do the same... must be same type of driving as well for both measurements.
if you see worse or no gains, you would benefit from other mods.
which mods to try will be just that, trial and error to see what works for your vehicle as they all respond differently to this stuff. Unfortunately there is no 'one cure for all' remedy here, however there have been enough member builds and experiments from which to obtain methods and ideas to apply to your own vehicle.
I hope this helps.
mike
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