Guys, I started taking parts on my stock 2007 EDM Evo 9 and I've seen something unusual.





Anyone else seen rear O2 sensor in this position? I was under the impression rear sensor is in the middle of the cat. How can this sensor work if it's before cat and it's only function is to confirm presence of cat and it's functioning?

 

Not sure about EDM set-ups but could you flip the cat the other way so it's at the very end rather than the beginning?

 

I thought about that, that it could be factory error and that the cat should be rotated 180, but the O2 sensor cable length would not allow it - so it was meant to be this way.
I don't understand how does it not throw a CEL with this configuration.

I have 88840016 ROM. Does it have rear O2 sensor check disabled by default?

 

The EDM model must be different because the USDM Evo IX does indeed have the o2 in the middle of the cat.

 

Do you also have front 02 sensor too?

 

Yes, front sensor is in its usual place - O2 housing

 

Looks like its installed backwards lmao
Post O2 sensor must be after cat or else it will not read the oxygen content coming out of the cat to compare to the pre O2 sensor..

 

Yeah sure looks that way, but I'm the first owner, exhaust was never been touched till now, O2 sensor wire length is just about right for this location (would not reach the other end of cat) and I've never seen CEL for this...

 

I just checked my oem cat and the o2 is mounted on in the centre of the cat... I have no idea whats going on here. Very interesting to find out what happend or why its like this if its correct...

 

Not sure if they're compatible but try finding a USDM evo 8 rear o2 sensor. I know it is A LOT longer than the evo 9 one and might be able to reach to the end since the o2 bung is in the midpipe on an evo 8.

 

I also have a 07 EDM IX and mine is the same position, same on my mates IX
I always found it strange aswell that they put it before the cat.

One tip: if you plan on putting a aftermarket exhaust on the car, buy a full TBE right away because the flanges will not line up otherwise, for some reason these are rotated completely different than on a USDM spec Evo.

To disable the rear O2 on 88840016 check this:
https://www.evolutionm.net/forums/ec...l#post10020636