Boxster catalytic converters - fix, replacement? - 986 Forum - The Community for Porsche Boxster & Cayman Owners

Hi All, Sorry if this has been discussed before, I couldn't find anything useful. Turns out the rattling noise that I've been chasing for a while is coming from one of my primary cats, the ceramics element fell apart and flies around inside the housing at acceleration. Bit strange, because there's no code, and last time when I checked (which was about 1000 miles ago because I don't drive the darn thing just work on it) the cat performance was fine. Anyways, questions: 1) Aftermarket or used, but original cats? 2) if the ceramic insert is dislocated, is there a way to cut the housing apart, fix it, then weld it back on (I guess not, but maybe) 3) Another long shot in the dark: anyone has heard of swapping the internals of a cat from a different car with similar shape (this sounds wild, I know). I quickly looked at the price for a new cat and wasn't a very pleasant feeling.. Any input is appreciated.

Are you absolutely sure it's the catalytic converter and not gravel bouncing around in the catalytic converter/exhaust heat shield?

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It is the primary cat that's one piece with the header. I think that has no shield. If you knock it with a hammer something rattles inside. I'm not looking forward to get it off, I wonder how many of the M8s are gonna snap.

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I'd be spraying penetrating oil on those bolts then, when ready to start removing them... try to remove one. Resistance? Apply the flame. Me? I'm applying that oil liberally, and a few times. Read long ago about removing a resistant nut/bolt. Recommendation was to try to, lightly, give the wrench some encourgement clockwise (tightening). Just enough encouragement to hear/feel the threads "give". I wouldn't give it but an eighth of a turn then backing off trying to emove the nut/bolt. Repeat. Had an E30 that had the rattling. Was unmistakeable... a cat. Good luck on the header removal!

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Thanks! I'll try the tightening/loosening method with some WD40. One bolt is already broken into the head so I don't have high hopes about the others. It's gonna be fun to drill it out since I don't have a lift. If they won't budge I might as well pull the engine, I wanted to do some work on it anyways.

Try a 50/50 mix of Acetone and trans. fluid such as the Dextron brand..... something red. Shake hell out of it before you apply it. Soak the bolt -nut for a day or two. Best thing I have ever used for rusted fasteners other then a torch.

Please do not even remotely think about using WD40. It has no useful properties in this application. Kroil or similar and heat are your friends.

Thanks for the tips, I invested into a can of Kroil, I'll try Blue's woodoo as well if all hell breaks lose

blue62's idea is not new, it was tested by Project Farm : It was also the cheapest option, by far. Good luck, mine all broke instantly.

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Nope.. not new at all it is what just about all shade tree mechanics used back in the 50's-60's. You can mix the Acetone with Marvel Mystery oil and that works well also. But I always have a little Trans. oil around so it is what I use. Just put it on the rusty bits generously and often over a few day period. The Acetone evaporates very quickly and it is what is taking the thinned Trans. oil down into the rust and threads. So don't be afraid to use plenty. Also make sure you shake it well each time you use it.

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Interesting, I've never heard about this. But I'm European, all cars are manual and no ATF sitting on the shelf, so it makes sense Always good to learn something new.

So, it seems like the aftermarket and used catalytic converters are in the same price range. Anyone with any experience/thoughts with either of these scenarios to share?

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I see you, as I, reside in Cali. Might want to look into the newer rules regarding cat convs. If correctly I remember, they must have special stickers/registration/? on them. Almost registered equipment. i don't know the details... look it up. Good luck.

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I am curious where can you get used cats are those are Not legally available in CA from the recycler yards.. (those yards, legally are not allow to sell used cats) yes it sucks..

I think one, as a Cali resident, miight hit AZ or NV and purchase from private sellers parting out thheir 986. Likewise Cali. I mean... if I were parting out my car I'm not reporting to anyone I sold the cats to an enthusiast.

Someone is selling a pair of cats for the Boxster for $500 which I think is a great price. Allegedly the car they were taken from had only 70k miles. I'll check them out tomorrow. Is there a way to get an idea about if they are indeed good condition? I can check the rattle, I can look into the honeycomb with a borescope for soot, anything else? Thanks for any tips!

OK, so I got lucky with removing the header bolts, I used some Kroil and they all came out easily. One was already broken into the head but I could remove it by hand... I found a used cat in L.A., here's the old and the replacement: I installed it and now there is no rattle, yayyy! I also looked at the efficiency of the new cat. Looks pretty good to me. Here's bank 2, for reference, also good: In the rattling one the post-cat signal sometimes was clearly following the pre-cat's signal. Didn't throw a code though. I uploaded a video of both here, just fyi: https://www.youtube.com/shorts/wrMxLf7S0Rc https://www.youtube.com/shorts/co477gS3rZE

Just wanted to share a few pics at the end of this thread. I shipped out the old catalytic converter to a recycling company and I cut it apart to reduce shipping cost which allowed me to take a look at the catalytic element. The honeycomb is seriously damaged, but surprisingly on the output side, and hence the rattle. I'm not sure what can cause this - some detonation? Or just aging? Interestingly, it was still doing its job, has never thrown a code, although the post-cat O2 sensor signal was not as flat as the same on the other bank..

Thanks for the follow up on this. Did your CAT rattle all the time? When hit with an object? My 2002 2.7L has an exhaust noise/rattle that occurs during acceleration once the exhaust warms up for about 10 minutes. When it's cold I can't make anything rattle when smacking with a rubber mallet. Heat shields are tight, so I'm thinking the matrix detaches from the CAT body when things heat up.

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I think it rattled already when I bought the car but iut wasn't so obvious because of all the other noises But it got progressively worse also. It was better when cold and was gotten louder with the engine warming up.