Those are AFR sensors (Air/Fuel Ratio sensors). They're a form of wideband oxygen sensor but are not compatible with EFIEs. See Tuning For Mileage
(towards the bottom of the page) for info on how to modify the data from these sensors.
Note, the 2 steady voltages of 2.4 and 2.8 are your signal lines. The ECU measures the current flow on those 2 wires and the sensor modifies the current to communicate to the ECU. The wire with the fluctuating voltage is your heater wire. AFR sensors run hotter than oxygen sensors, and need to be in a more precise heat band, therefore the heater voltage fluctuates as needed to maintain that heat.