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O2 sensor
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evans80 Offline

Posts: 2
Joined: Apr 2008
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Post: #1
O2 sensor
I have a 2005 Subaru with HHO input, one into the vacume line and one into the intake past the MAP and a MAP control and two 1/2 inch extensions on each O2 sensor. I am only getting about 5 mpg more from 25 to 30 MPG. I cannot change the MAP control much without getting a check engine light. I have a Scan 11 so that is no problem to clear. I am in electronics so I checked the O2 sensor lines, 4 of them, one black wire has + 12 volts steady and one blue has+ 2.825 steady volts, another white wire has +2.473 volts steady and the last black wire changes from + 5 volts to 12 volts quickly. All readings with engine running up and down rpm. Wife runs foot feed.
My question is which wire is the signal wire?? Only one wire changed with engine running but I have read nothing about an O2 sensor changing with that much voltage. Any information you might have would be appreciated.
04-12-2008 03:26 PM
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mike Offline
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Joined: Jul 2007
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Post: #2
RE: O2 sensor
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.

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04-12-2008 03:58 PM
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