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Discussion Starter #1 (Edited)
Thanks to Southpark for helping me figure out how to route the O2 cable for this DIY.

The 323i came with this lame single pipe exhaust that restricts airflow and you can't bolt on a aftermarket exhaust to.

Look how lame it is. :thumbdwn:

After passively looking on CL for a few months I got a OBD2 328i exhaust for 60$

To perform this swap you are going to need:
  1. 328i OBD2 midpipe and muffler
  2. Manifold to Midpipe Gasket 18301716888 X2
  3. Manifold to Midpipe Nut 18301737774 X6
  4. Muffler Install Kit 18210146036

Step 1

Rip out the old exhaust

Don't bother disconnecting the mid pipe and muffler. Put the jack on the muffler and remove the muffler bracket bolts. Mine just crumbled away. Put a bucket under the muffler to hold it. Jack up the cat to remove the mid pipe hangers. Unplug both O2 sensors. Unbolt the support bar and undo the 6 nuts holding the mid pipe to the manifold. Then jack up the muffler again and remove the bucket. Drop the muffler and give it a yank. The entire exhaust should slam down.

Note: Soak the mid pipe to manifold bolts in penetrating oil. You do not want to break a stud.

Step 2

Relocate the pre-cat O2 plug.

Remove the plug from the clip and toss it over the trans support.

The cable is zip tied to the trans with some other cable. I took a screw driver and broke the zip tie.

Then pull the cable along the trans until you get to a metal clip holding a few wires in. Use a screw driver and push the clip open while pulling the O2 cable out.

On the engine there is a zip tie holding the O2 cable with a few other cables. Break it off with a screw driver.

Follow the cable over the front cross member and pull it across. It is in a group of other wires. Then use the brittleness of the sleeve the cable is it to push it up to the engine bay.

Pull all of the slack up and route the cable behind the plastic engine cover. Then push it down near the manifolds.

Step 3

Install the O2 sensors

Using a 22mm or 7/8 box wrench remove the O2 sensors off your old exhaust while noting which one is the pre and post cat sensor.

Take that same wrench and remove the plug on the manifold. You can only really remove the plug on one of the manifolds. Put your pre-cat O2 sensor in the new hole. Plug the sensor in and zip tie the cable out of the way.

Take the plug and put it in the opposite side of pipe that you put the pre-cat O2 in.

Then put the post-cat O2 sensor in the other hole.

Step 4

Bolt up the new exhaust

Installation is the same as the removal except you install the mid section and the muffler separately.

Wire up the post-car O2 like this.

Step 5

Give it a Brap

Make sure to check for leaks!
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