The basic question here is will I need 1 Dual EFIE or 2 Dual EFIE's?
I have a Mazda Tribute V6 2005. It has 4 O2 Sensors.
I'm installing an HHO system and thinking about the EFIE option.
This is directly from the Haynes Manual for my vehicle:
"On the V6 model there are 4 heated O2 sensors, one upstream and one downstream for each cylinder head. There are three catalysts; a smaller "fast-light-off" cat right below each exhaust manifold and another larger downstream catalyst. The O2 sensors are located upstream and downstream in relation to the two smaller catalysts." The "fast-light-off" cat are actually an integral part of the exhaust manifolds.
Thus it the layout is like this for one of the cylinders (note this would be times 2 - 2 cylinder heads for the V6 model)
Engine --> Beginning of Exhaust Manifold --> Upstream O2 Sensor --> "fast light-off" cat --> downstream O2 Sensor --> large conventional 3-way catalytic converter (TWC) or as stated above the "larger downstream catalystâ€.
Basically all the documentation on this site says that you need and EFIE for ALL O2 that are upstream of the catalytic converter... well TECHNICALLY all 4 of my sensors are upstream of the conventional catalytic converter.
It's just on my vehicle they have inserted a "fast light-off" cat between which is separating the O2 sensors.
Note that there is nothing (no O2 sensors) after the conventional cat converter.

So do I need TWO dual EFIEs for the upstream and downstream sensors (one on each side)? OR do I just need ONE dual EFIE for just the two upstream O2 sensors?
I guess a bit more detailed info on your site would help explain this. Maybe a few diagrams of the possible layouts and O2 combinations showing where the EFIE would attached might be a good addition… just a thought.