In most vehicles larger and more consistent MPG gains can be achieved by using a O2 extenders in conjunction with your Hydrogen Generator and Delivery System. In fact these inexpensive devices will work even if aren’t running these systems.
Contrary to it's name this sensor actually measures the air/fuel ratio not the amount of
O2. The sensor is a catalytic converter with a thermocouple so the sensor generates voltage based on the heat from the conversion of unburned fuel and available Oxygen to CO2 (an exothermic reaction). Since Hydrogen extends the lean operating range less fuel and less oxygen are available to be converted by the O2 sensor to heat resulting in a lower voltage output.
These adaptors adjust the front O2 sensors to the top of the exhaust manifold where there is more Fuel and O2 are located (Remember being told in grade school in case of a fire to crawl, because the vapors rise. We are just taking advantage of this principle.)