E36 323i exhaust swap problems (US Spec)

[Ozzyman22]

Swapped my exhaust on my 99 323ic from stock midpipe and muffler to a midpipe from an m3 and AA cat back. Now receiving code P0133 and getting worse mpg since.

US spec 323s had only 2 o2 sensors one before and after the cat while m3s had 4. 2 on each headers and 2 behind each car

For my swap I put my pre cat o2 sensor on one of the headers and the post cat on the opposite piped and am still getting check engine issues.

I’m not sure what to do at this point and am lost because I thought I followed the steps you had to for this swap to work. I just need help before I just bring it to specialist and have to pay for them to tell me what’s already wrong.

Any advice from anybody whose done this before will be greatly appreciated.

P.S. this was the link I followed where I first saw this done on a 323. https://motoiq.com/project-e36-323is-building-the-poor-mans-m3-part-4-exhaust/?unapproved=103237&moderation-hash=fd0ca2764be4acfa8ae96d83d68a6d90#comment-103237


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[tiMASTER]

If you are only reading one pipe (one bank) I think your post cat should be on the same pipe as the pre cat.

DME is probably getting g data outside tolerance now since it’s comparing two different gas streams. Maybe one cylinder is using oil and the sensor is seeing this difference…

Not sure but I’d try moving the downstream sensor to the other pipe and (clear codes) see if it improves.

[Ozzyman22]

If you are only reading one pipe (one bank) I think your post cat should be on the same pipe as the pre cat.

DME is probably getting g data outside tolerance now since it’s comparing two different gas streams. Maybe one cylinder is using oil and the sensor is seeing this difference…

Not sure but I’d try moving the downstream sensor to the other pipe and (clear codes) see if it improves.

You think so? I saw on other places that you should have em on opposite sides so each pipe can be read?


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[tiMASTER]

I think so because the DME is looking for CAT efficiency as well as raw data.

Swapping down stream and giving it a try shouldn’t be too bad- easier than upstream ones. In a low mileage engine it might not matter they are in Different pipes.

[Ozzyman22]

I think so because the DME is looking for CAT efficiency as well as raw data.

Swapping down stream and giving it a try shouldn’t be too bad- easier than upstream ones. In a low mileage engine it might not matter they are in Different pipes.

You might be onto something, I’m going to take it my local specialist that I have a good relationship with and ask for their advice


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[Ozzyman22]

I think so because the DME is looking for CAT efficiency as well as raw data.

Swapping down stream and giving it a try shouldn’t be too bad- easier than upstream ones. In a low mileage engine it might not matter they are in Different pipes.

Figured out the issue, wrong o2 sensor was plugged in.


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