New Exhaust OBX RACING

[cali yaris]

^ The two sensors are not the same. Technically, the first one is more of an air/fuel sensor (though it's kind of a weird hybrid design by the way the ECU reads the voltages) and the second one is an O2 sensor to monitor the cat. Pretty sure that's all it does.

Why would you move it downstream?
And why would you want it to be "warmer"?

[07stlYaris]

Downstream past the Cat. Catalytic converters function better at higher temps leading to a more accurate reading for the O2 sensor. Higher temps within reason of course. I've seen melted catalyst in engines that ran waayy too lean. Anyway, thanks for the clarity on the sensors.

[CTScott]

Originally Posted by cali yaris

^ The two sensors are not the same. Technically, the first one is more of an air/fuel sensor (though it's kind of a weird hybrid design by the way the ECU reads the voltages) and the second one is an O2 sensor to monitor the cat. Pretty sure that's all it does.

Why would you move it downstream?
And why would you want it to be "warmer"?

They are both platinum coated zirconia sensors, but the Air/Fuel sensor has the ability to detect the ratio over a wide range (i.e wide band sensor). The heated O2 sensor can only detect that the AFR is at stoich or is rich or lean - It can not detect how rich or lean it is.

So, the air/fuel sensor before the cat allows the ECM to precisely control the ratio and the heated O2 sensor after the cat allows the ECM to monitor that the fuel ratio is properly adjusted to allow optimal operation of the 3 stage cat (which performs best at an AFR of 14.7).