I decided to drive the car till the check engine light came on after installing my Cat-back. It went about 50 miles. I had a muffler shop weld my original threaded bung for the sensor and nut for the little guard. After that I took it to an import mechanic with a computer to see what the readings were and to ask him if the sensor affected the air/fuel. He said the cars ECU reads o2 in the exhaust and does in fact adjust the fuel mixture. He rev'ed the motor a few times and had me watch the screen and the readout changes constantly with whatever load is on the motor. Even while idling the readouts are always moving. He said if the sensors are bad the readout stays level. Also, it is for emissions, not neccesarily power. So there's another opinion.

 

OBDII vehicles have several O2 sensors, though. The O2 sensors closest to your exhaust ports are the ones which the ECU monitors to adjust for the fuel supply. The one after the cat is not used for the fuel supply.

 

So when my apexi gets here (if it ever does) do you think that I should just forget about the second O2 sensor and not use it?

 

it might cause the check engine light to go off, it might not. it's not hard to have the exhaust shop drill and tap an opening for the 2nd sensor.

 

took them about 15 minutes. 20 bucks.