Im in the middle of a header install, but the stock setup had 4 o2 sensors, and now i only have holes for 2 with my offroad y pipe. which O2 sensors do i use and which harness do i plug them into, the fronts or the rear harness. thanx

 

I believe you have to connect them to the front ones because those are the ones that measure your A/F ratio and give feedback to the PCM if it is running lean or rich. The rear 02s are for emissions purposes only. As for which ones to use I would just go with the original.

 

Yep use any 2 sendors that suit you and hook them to the front harness points. You'll need wiring extensions to do this and your check engine light will be on due to the rear ones not working.

 

Ok good, because i guessed and used the front plugs. Thanx

 

If you aren't getting a tune, just have another set of bungs welded on and then plug all 4 sensors in.

-Geoff

 

This is an old thread but if you havnt fixed your rear O2 sensor problem I will sell you my simulators. I never even used them because I got mine tuned out a week after I bought them...