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DIY: Do It Yourself
Post here to share or improve your wrench turning skills! All BMW E46 DIY tips, tales, and projects discussed inside. Learn to work on your car and know the right BMW parts you will need!

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Old 07-04-2012, 03:48 PM   #1
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Join Date: Mar 2004
Location: Atlanta
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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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Old 07-04-2012, 03:58 PM   #2
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*Step 3- remove the driver's side engine mount. 16mm nut on bottom of control arm and 16mm nut on top of mount seen from above. Remove 4 13mm bolts and whole mount comes off of side of engine block. Also a thick grounding wire via 13mm nut to car frame.

*Step4- Guess this should almost be step 1!! I had a garage remove the rusted exhaust pipe to manifold nuts for me last year and change a frozen o2 sensor for me, so I didn't have to struggle. Removing the 4 exhuaust nuts will be the hardest part for most DIYers.

*Step 5- remove the top o2 sensors for easy removal of manifolds/cats.

*Step 6- you can now easily see most of the manifold nuts from the bottom of the car. The only ones not accessable from the bottom are the top nuts on the forward manifold. A 1/4" rachets w/ 11/2" extension and 11mm deep well socket was the perfect fit to get these off. I originally tried a 3/8" rachet and 3" extension and struggled for too long. I used the racheting 11mm box end wrench for the very back nut on the rear manifold. You must remove the front manifold 1st to gain easier access to the rear manifold.

pic 1- what it looks like underneath... easy access! pic2- some studs come out w/ nut. I replaced these. pic3- racheting box end on rear nut pic4- wrestling w/ top nuts pic-5- closeup shot of socket on top nut. NOTE the downward angle of the engine block and manifold studs. pic6- front manifold removed
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Last edited by beberle; 07-04-2012 at 04:11 PM.
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Old 07-04-2012, 04:33 PM   #3
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*Step 7- install rear manifold/cat and then front manifold. The new manifolds do not come w/ pressed studs like the factory cats. It's easier to install this way. I could get a torque wrench on most of the nuts. The ones I couldn't, I attempted to hand-tighten to match the others. Another benefit of using a 1/4" drive is that it takes a good bit of force to get 15ft/lbs and not break a mounting stud! - Note: it's easier to install the rear o2 sensors on the manifolds BEFORE mounting the manifolds to the block. No clearance problems. the front o2 is easily installed from top.

*Step 8- I found almost no play w/ the manifolds sitting on the mounting studs. Luckily, these aftermarkets pieces fit pretty well! However, there was a 1/4" difference in manfold lenghts between the two. Luckily I was able to put a couple washers under the little manifold cross-brace to level them out. Tightening the nuts pulled the rear pipe into position.
-The rear manifold required 3/8x11/2" and 3/8"x2" bolts with associated nuts and lock washers. Don't use stainless steel, it supposedly stretches when hot. I used grade-5 hardware. The rear Pace Setter was threaded for a 3/8" Standard thread in the flange, so no nuts required, but I used a lock washer under the bolt head. Two 3/8x11/2" bolts.

Step 9- put everything back together. Engine mount. frame brace. secondary air pump. That's it! I had disconnected the battery prior to work, so I cleared the codes and the car was ready to re-map to the new cats when I was done.

No more check engine lights! These cheaper after-market cats have a 2-year warranty; I hope they go for at least 4! It took me about 7 hours over the weekend. I hope this DIY saves you some time. Now, Here's hoping I can make it to 300k

pic 1- gap between two manifolds pic2- gap solved w/ washers pic3- new studs replacing ones that came out pic4- pretty new manifolds/cats installed!!
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Last edited by beberle; 07-04-2012 at 04:40 PM.
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Old 01-22-2013, 09:35 PM   #4
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im having a problem with the gap but im using ebay headers.... not even flush but piping of the headers are hitting the engine mount bracket in 1 place so I dont know if I put the bracket in the wrong holes or the piping is ****ed up and wont let the exhaust manifold drop down wear it should and if so it would be putting strains on the studs for the manifold and next speed bump or pot hole can really cause some damage
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Old 08-08-2014, 02:44 PM   #5
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Thanks for the great post.
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Old 07-19-2012, 04:28 PM   #6
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Great post
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Old 09-16-2012, 12:26 PM   #7
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Should step #3 be passenger side motor mount?
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Old 08-08-2014, 05:49 PM   #8
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Thanks for posting .... long term / high mileage owners will need to address this at some point.
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Old 04-27-2015, 09:36 AM   #9
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What was the code for the Catalytic converter? was it P16A7 ?
Also how do you know which Catalytic converter to replace?

Last edited by 2005 e46; 04-27-2015 at 09:37 AM.
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Old 05-31-2015, 03:03 PM   #10
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You said the one of the pacesetter manifolds didn't fit, do they not make the correct one? Why did you go with another brand? Great DIY thanks!
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Old 01-21-2016, 10:36 AM   #11
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Good write up! Will be using it this weekend . How tight do the exhaust manifuld studs/nuts have to be tightened?
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