That’s actually a really good question, highlighting a common misconception.
Many people are aware that extra oxygen in the exhaust causes the computer to richen fuel mixtures… And that the EFIE is designed to ‘correct’ the oxygen sensor output so that the computer doesn’t know there’s ‘extra’ oxygen in the exhaust.
But they are not aware of WHY there is extra oxygen in the exhaust.
It isn’t because of the oxygen that is being fed in with the Brown’s Gas (aka BG or HHO). Some people think just adding pure hydrogen will solve the ‘extra oxygen’ issue don’t understand the real issue.
Just to give you some perspective, on a 5 liter V8 engine, about 5 liters per hour (not per minute) of BG (HHO) from one of our HyZors is enough to give most vehicles a 25% reduction in fuel consumption.
Of that 5 liters/hr of BG, only about 1.67 liters is oxygen. A 5 liter engine, running at 1800 rpm, will pump 35,100 liters of air per hour, of which about 7020 liters is oxygen… So you can see that a couple of liters of oxygen being inserted from an electrolyzer will make virtually no difference to the engine’s exhaust oxygen content.
In fact, feeding in pure hydrogen will STILL increase exhaust oxygen, because it increases combustion efficiency, even though pure hydrogen won’t work as well as BG (HHO) because pure hydrogen lacks certain constituents that further increase combustion efficiency, like water vapor and ExW.
…so just feeding in pure hydrogen isn’t the answer to lowering exhaust oxygen.
What increases exhaust oxygen content is EFFICIENCY of combustion! Anything that increases combustion efficiency (including adding hydrogen) will increase exhaust oxygen content.
The ‘increased’ oxygen comes from three major ‘sources’.
First, if you are using less fuel, less oxygen gets ‘burned’ and thus there’s ‘more’ in the exhaust.
Second, when increasing combustion efficiency, the Carbon Dioxide (CO2) rises slightly but the Carbon Monoxide (CO) drops off to near nothing, so oxygen that was tied up as Carbon Monoxide is free and causes exhaust oxygen to ‘rise’.
Third, combustion happening more efficiently will reduce Oxides of Nitrogen (NOx) so oxygen that was tied up as NOx is freed up and exhaust oxygen content ‘rises’.
You can learn more about combustion efficiency in my ‘Double Mileage, Guaranteed’ eBook.
So any technology that increases combustion efficiency WILL cause a rise in exhaust oxygen and, if you have oxygen sensors, you WILL need a EFIE on each one to compensate.
Note that oxygen sensors are often biased to assume you are burning a certain amount of fuel. When experimenting with my HyCO 2A system, I tripled the mileage of my 345 ci engine in a 1974 International 4×4 crewcab 3/4 ton truck with a box on the back. It went from 7 mpg to 23 mpg… And the oxygen sensor was reading as little as -200 mV! Negative millivolts means that there was more oxygen in the exhaust than in the outside air, which is impossible of course, so indicates the bias I’m talking about.
So my answer is YES YOU NEED an EFIE! It doesn’t matter what technology you use to increase combustion efficiency (like vapor fuel, hydrogen, BG, water injection, acxitone, etc.) you will need an EFIE on each of your oxygen sensors; and maybe some other Combustion Enhancement Interface Technology (CEIT) like MAP Enhancers, IT Enhancer, Carburetor Enhancer, ED, etc.
NOTE: It can occasionally happen that when combustion enhancement is added, the exhaust oxygen rises (that always happens) and the computer does NOT increase the fuel. In these cases the EFIE is not needed. This usually happens when (for some reason) the computer’s oxygen sensor feedback programming is not working.
So if someone tried their technology on such a vehicle and it worked without an EFIE, they might assume they don’t need an EFIE on any vehicle; and that’s an incorrect assumption. If the oxygen sensor feedback programming is working, you need an EFIE(s) on your oxygen sensor(s).
NOTE: It’s possible (assuming your oxygen sensor feedback programming is working) to reduce your fuel consumption by as much as 10% by adding the EFIE alone (with no combustion enhancement technology), by slightly leaning your fuel mixture, so it pays to add an EFIE in any case.