I have an m2 dual tip and when getting the car tuned last weekend I had a weird problem. First the o2 sensor was put in one tailpipe and the afr readings were in the 10s through 3-4k rpm, then 13s then 14s, then exactly at 6k it shot up to 18 afr! We tried it multiple times and the same thing occurred. Then we put the o2 sensor in the other tail pipe and got stable afr in the 10's and tuned it from there. So my question is why would the afr readings be that off in one tailpipe versus the other? the exhaust has about 4k miles on it and as far as other exhaust mods go I have a downpipe and resonated midpipe. does this indicate I have something wrong with my exhaust?

 

you might want to check for a leak in your exhause system. the wack reading could be coming from air leaking in the exhause form a seal or something. put the car on a rack while running the engine and move your hand down the exhause pipe ( dont burn yourself) and look for a suction of air or pressurizied air some where. also listen for the leak you can sometimes hear them. its is definatley after the turbo assembly so it will not affect performance just your o2 readings.

 

an exhaust leak should screw up the afr readings regardless of which tailpipe you put the o2 sensor in right?

 

wait wait, you're putting the O2 sensor in the tips of your exhaust? you're supposed to put them up in the downpipe or the exhaust, wherever your O2 bung is in your exhaust system.

 

Tailpipe placement is fine for full power runs but not idle , or cruising with tail winds. We have verified this by testing. DP placement also shortins O2 sensor life due to high temperatures.

Exhuast leaks do not affect AFRS as the sytem is under pressure and just reduces flow rate a little out the tail pipe.

Too much unverified hearsay!

 

So if there is no exhaust leak, which so far I cannot find one, then there might be something buildup maybe inside the exhaust?

 

you have 2 tips there on the muffler and one pipe as the source. the mufflers main job is to quiet the sound. what you are seeing may be a bit of reversion in the muffler tip from one side to the other sort of a venturi effect going on. just a guess. i have always belived that an exhaust leak will register a bit lean as the exhaust is not under constant pressure but a series of pulses that have a vac created behind them which will draw in a bit of air

 

The affect is only fully true on open straight exhausts without turbos.

With turbos and cat backs, they both interfer, chop up, and smooth out the pulses.