I just had a new exhaust installed, MAP O2 Eliminator downpipe, to a Megan test pipe, to a Greddy Full Race Titanium. My installer said that there was no good place to install the stock rear O2 with the Megan pipe, he said if he has the O2 bung near the downpipe, the sensor would hit the drive shaft, so he flipped it around with the O2 bung near the catback, but it faces down in that position, towards the road. The solution right now was to plug the bung and use the bung on the Greddy exhaust, but this moves my rear O2 back about a foor or more farther than stock. The car was misfiring when it was cold the other night, so my friend installed his HKS DLI, which cleared that up.

Anyway, are there any issues with installing the rear O2 that far back in the exhaust stream? I haven't driven the car since the work was done, it's sitting at my friends house with a fuel leak, but I wanted to do some research on the rear O2 placement. Any comments or advice is welcome, thanks guys!

 

From I understand, you dont really need the O2 sensor when you have aftermarket exhaust, CEL is always going to come on w/o CEL fixed, most of the tuners usually turns it off anways. Best bet if you want to save money, a dummy will the best thing to do.

 

This is why I dont buy from Megan......
But it doesnt really matter if the O2 sensor is further back. Theres no cat so it doesnt really matter. But you will get a SES light if you dont buy those anti-foulers to trick the sensor. Or with a tune, the tuner can elimanate it.
This is why i went with SpeedCircuit. Has CEL/SES fix built into it already, and an extra bung for wideband O2.
http://www.speedcircuit.net/product_...6a1f3259badc47

 

the rear O2 is solely used to check catalyst efficiency. The rear O2 had nothing to do with your misfire. the rear O2 is also heated, so it can be mounted anywhere. just make sure it doesn't hit stuff.

 

Thanks for the advice guys. I won't worry about the rear O2 at all.