I am getting into tuning my 04 lancer and wonder what is best place for wideband sensor in the stock exhaust? I do have cat back but if i put sensor in sensor 2 spot its reading after cat exhaust.

 

before the cat

 

Technically speaking, your downstream O2 is in the inlet of the cat, so it's actually before the cat. But I wouldn't recommend putting it there since you'll throw a light. Best place would be around 10" from the manifold

 

My lancer has manifold type cat. the upstream bung is less than 18" and the downstream is after cat so readings will be skewed. was just wondering if the upstream bung would damage wide band.

i want to stay legal for now but would like to tune with the wideband.

 

Oh I got ya bro. I thought you were talking about the cat under the car. You can't use the upstream location because the Ecu uses that for closed loop. You're better off having a bung put in the downpipe somewhere between both oxygen sensors, or if you're really desperate. Use the downstream location and turn the O2 off in Ecu flash

 

I am just worried about getting incorrect afr from after cat exhaust. I JUST GOT STARTED DOING ECUFLASH ON MY CAR AND LEARNING. THE REAR O2 HAS NON FOULERS TO LIE TO ECU RIGHT NOW BECAUSE CAT IS BELOW 96% EFFICIENT.

 

I think you'd be ok for what you're doing. If you ever go to a professional tuner, their wideband is on the back of the exhaust. As long as you keep it close to the header, it shouldn't cause a problem. I'd really recommend getting an aftermarket header though. Would really free up the airflow on the back of the motor. Out of anything I did to my lancer before going turbo, I noticed that the most. With ecuflash, you'll be able to shut off the rear O2 in the periphery bits. So you wouldn't even need the anti foulers anymore