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Old 07-04-2012, 03:48 PM   #1
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Join Date: Mar 2004
Location: Atlanta
Posts: 181
My Ride: 2009 328 wagon
catalytic converter/exhaust manifold replacement DIY

It's been a couple days since I finished replacing my catalytic converters, and now I have a little energy built up to write up the DIY ;-)

I'd say this is a 7 on a 1-10 scale of difficulty. Nothing crazy, just lots of pieces! Most importantly, I advise any long-term BMW owner to purchase an engine-support for maintenance on their car. I bought mine from Harbor Freight for $80 and used it to change out motor mounts a few months ago. It comes in handy for changing cats as well as oil pan gaskets... something everyone with a car over 100k miles will soon have to do.
FYI, my 2000 323it has 240k miles on it. The cats went out around 235k. I changed O2 sensors around 120k and then again at 230k when I got O2 sensor codes. As soon as I swapped them this time, the Catalytic converter inneficiency code poped up... oh oh!!

* Parts: I purchased Pace Setter cats on eBay for $300 each. Turns out I accidentally ordered the wrong front cat/manifold. The manifold for 2001-2005 325 does NOT fit the 98-2000 328/323 front manifold. Pictures show why. I couldn't find the correct Pace Setter front, so bought unknown brand front manifold from BavAuto for $360. Also buy 16 new exhaust manifold nuts and a handful of studs, as well as new gaskets for the engine-to-manifold as well as manifold-to-exhaust pipes. Nuts and gaskets MUCH cheaper online. Dealer is outrageous.
* Tools: As mentioned, the engine support/brace is worth its weight in gold. Also, a 1/4" socket wrench, a 11/2" extension, and 11mm deep well socket will get most of the manifold nuts off. A 11mm racheting box end wrench really saved the day for a couple nuts on the rear manifold. Various other 13mm & 16mm sockets are used for the rest.
I'm skipping the basic steps that other DIYs cover.

* Step 1- Remove the plastic engine cover (to access O2 plugs), and cabin filter housing like we've done a million times before. Remove the Secondary air pump/smog pump as well as the valve on the engine block and associated hoses. This only takes a couple minutes w/ a 10mm socket and really opens up access to the top of the manifolds. NOTE: remove the air pump mounting bracket as well (3 10mm nuts). I kept hitting my knuckles on the bracket and realized how easy it was to get out of the way.

*Step 2- Jack the car up. Remove the frame cross-brace w/ the 4 16mm bolts for access to the bottom of the manifold. Use the engine support/brace and just jack the engine up engouh to take the weight of the motor mounts (1/4").
Remove the driver's side motor mount.

pic1- engine support, pic2- air pump mount, pic3- pump mount removed, pic4- wrong front manifold, pic5- correct manifold
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Last edited by beberle; 07-05-2012 at 07:23 AM.
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