All the Brown's gas systems do is increase the ambient air quality with free oxygen and hydrogen molecules. This has the effect of altering the combustion, and the O2 sensors detect this. In most cars, this is in concert with the loop of sensors that includes the Mass Air Flow sensor, which tells the computer how much air is passing into the motor. The MAF can be recalibrated to compensate for the added fuel (H) and air (O) and the car will run more efficiently. The side effect is that if the HHO system isn't running properly, the computer is forced to compensate, again becoming less efficient by thinking that the HHO system is still operating and adjusting the A/F ratio. An effective way to eliminate this issue is to replace the entire computer with a wide-band system that can recognize and adjust for large variances in A/F ratio. Not cheap, but doable.
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