Great How

Chasing mileage 1

Notes:
Front O2 sensor labeled on the wiring diagram as an “air fuel ratio sensor”.
Rear O2 sensor labeled on the wiring diagram as “Rear O2 sensor”.
According to the repair manual the rear sensor is only used to monitor the status of the converter and to predict its possible failure.

A little background:
Installed an HHO system on my 2006 Subaru Turbo Auto and have not been able to get any gains in mileage. Installed a MAP adjuster with no gains and then a MAF adjuster and still no gains even when using the two together. I will see an initial gain when resetting the ECU but after it learns the gains go away. So now it is time to hail to the Chief of Sensors, the O2 sensor.

Was advised that since the car has an AF Ratio sensor a standard EFIE will not work and that an inline resistor should be installed, somewhere in the 7-30 ohm range. Installed a 14 ohm resistor and saw my mileage change but for the worse. Usually get about 22mpg in mixed driving, with the resistor installed mileage was 17.5mpg. My EGT’s were also down by over 100 degrees from my baseline tests also confirming I was running richer.

Description of the video:
The front O2 sensor (the AF Ratio sensor) has been disconnected from the ECU and a DVOM is connected to the blue (as positive) and white (as negative) wires on the sensor. There are two other black wires which are used for the heater, these are also disconnected from the ECU but not conencted to anything in the video. The connector from the ECU to the AF sensor is just dangling at this point.
The software running is ECUEdit and I am displaying the Rear O2 sensor’s millivolts via the ODB2 connector. You’ll also note that other readings on the computer screen don’t change, this is because the ECU is not receiving feedback from the front O2 sensor and is running a base map instead.
The MAF adjuster mentioned in the video is an adjustable POT that when activated tells the ECU there is less air flowing in to the engine, this causes the ECU to slow the feed of fuel into the engine effectively leaning the mixture. You will see that both the AF Ratio sensor and the rear O2 sensor react similarly with the front sensor reacting first and much faster. Based on my findings shown in the video I will be installing a ‘traditional EFIE’ this weekend.

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