ML 270 CDI Front Catalytic Converter Rattle

soup nazi

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Hi Chaps
I have recently had the rear Cat removed from my ML due to blockage. Fuel consumption has dropped by 2.0 litres per 100km, nice!

I now have a rattle/vibration that seems to be getting worse coming from the front cat area. It sounds like the ceramic is vibrating inside the casing. Have any of you had any problems with the front cat at all?
 

Alex Crow

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The usual blocked cat scenario on the ML270 where the second cat is blocked, starts with the first coming loose. It slides back in the housing, and abrades against the rear face, generating debris that then goes on to block the second cat.

Hence I would not be surprised if the first cat is loose.
 
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soup nazi

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OK, so what would be the best course of action here. Cut the the cat out altogether and replace with a straight through pipe, try and fit a straight through pipe into the existing cat so it all looks as it is or replace the cat with a new one (expensive at a guess)??

Has anyone just busted the ceramic out of the existing cat and refitted it hollow? I'm thinking this might make some weird noise?

SN
 
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Alex Crow

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Yes, all options possible.
Knocking out the cat is a fair plan, and should still be OK for MOT testing.
 

panason1c

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Empty the first cat, you might get a resonance from the empty cannister which can be remedied by fitting a straight thru pipe.

It definitely will not affect the emisions readings for an MOT.
 

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as above. simply break the ceramic part inside the cat and empty it out from the box. ive just done both of mine on the 203 and apart from the turbo whistle being a little more audible with the windows down, i cant say ive really noticed much difference in the way it sounds
 

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Has anyone tried to secure a rattling ceramic block inside the CAT by using a few long stainless screws? Bit of a bodge I know, but just wonder if it would work and for how long. I thought of trying that but never got around to it - was away anyway when problem originated.
Only asking as that would be a lot easier to do without even removing the cat than trying to remove the whole apparatus, cutting it apart, removing the insides and then trying to get it all back together again, unless you happen to be a heck of a welder (stainless steel) and have a lift/hoist.
 
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soup nazi

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Has anyone tried to secure a rattling ceramic block inside the CAT by using a few long stainless screws? Bit of a bodge I know, but just wonder if it would work and for how long. I thought of trying that but never got around to it - was away anyway when problem originated.
Only asking as that would be a lot easier to do without even removing the cat than trying to remove the whole apparatus, cutting it apart, removing the insides and then trying to get it all back together again, unless you happen to be a heck of a welder (stainless steel) and have a lift/hoist.

Oigle
I think the ceramic would just vibrate and crack up. Once it starts to rattle it would be hard to stop. I will try to knock the ceramic out of the front converter but i'm not sure that will be as easy as it sounds. Also it may create some sort of hollow sound and that's my biggest worry. I was hoping someone else had already tried it. Getting an exhaust guy to cut it out is preferred but they don't seen too willing. I wont even bother asking benz for a quote on a newy. Surely efter this i'll get a clean run for a while?????
 

oigle

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Oigle
I think the ceramic would just vibrate and crack up. Once it starts to rattle it would be hard to stop. I will try to knock the ceramic out of the front converter but i'm not sure that will be as easy as it sounds. Also it may create some sort of hollow sound and that's my biggest worry. I was hoping someone else had already tried it. Getting an exhaust guy to cut it out is preferred but they don't seen too willing. I wont even bother asking benz for a quote on a newy. Surely efter this i'll get a clean run for a while?????

Yes - you won't get an exhaust guy to take the front one out. Big fines if caught. There are legal aftermarket ones available for much smaller money than OE.
You are probably right about the ceramic vibrating and breaking out of the screws. Just a wayward thought. Another one I had (bad dreams?) was to drill the casing and inject clear silicone into it in a number of places to take up the gaps formed by the cat vibrating. Might sound silly but, when I was turbo car racing/developing, we used clear silicone as the manifold gasket on many a very hot turbo engine with perfect results - redhot manifolds didn't worry it at all. I'd be quite prepared to believe that it could fill the gaps in there and hold the ceramic in place for many a month/year. Would take all of maybe 30 minutes to try it. Nothing to lose. Need to let it setoff for a few hours before running the motor.
When I removed the secondary cat, I cut it open and the ceramic block was quite intact. Just seemed that it had come loose from the surrounding metal and vibrated when idling.
 
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soup nazi

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Oigle
I have been told a lot of after market jap cats are rubbish and block up after only 10,000km or so. What I might do is get a quote on replacement with a euro cat, bash the guts out of mine and if it makes any noise, go for the new cat! I could inject stuff into it but I would have to take it off to get all round it and somehow seal the holes again after. Seems a bit messy. My preference is no cats at all if possible. This is where the backyard dodgy brothers exhaust man may come in handy!!!
 

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Cats or not to Cat

My ML 270 started the cat to rattle like crazy and it was driving me mad SO.
I had my local garage guy cut open the cylinder and remove the offending bits and re-weld the cylinder again.
I also had him bash out the front cat from the canister and replace the hollow can and the car runs much better and I have never had a problem with the test and emissions.
I am afraid I am a non believer in trying to save the world with all this c**p about emissions, Co2 and the like, man cannot change the weather if he tried nor the world, all this is just a great tax wheeze grasped with both hands by the ruling classes, toffs who have never had to get up early in the morning make the sandwiches and drive in the snow and rain to start work at 07.00 am for a 12 hour shift.
All they want to do is to relieve us of as much money as they can so as to support them in the way they have got accustomed to. (rant over).
I am afraid that cats tend not to work well in our cold damp climes, that is why the manufacturers have started fitting them right up to the manifold to try and get them hot enough to work.
This will NEVER work in the average town run as the cats never get hot enough.
As for the DPFs now fitted I will not even start.
Mike
 
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soup nazi

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Muller 1
Thanks for the insight. I have to agree with you that all this is just another way to relieve us of our hard earned. I'm gone do what you did and bash the guts out of the front cat and refit it empty. Will report the results. I will call it a Catectomy!
 

oigle

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Muller 1
Thanks for the insight. I have to agree with you that all this is just another way to relieve us of our hard earned. I'm gone do what you did and bash the guts out of the front cat and refit it empty. Will report the results. I will call it a Catectomy!

How did you go with the catectomy?
 
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soup nazi

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Catectomy planned for Monday morning, will advise!
 

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I did clear the centre cat to remove the blockage as in photos, then I noticed the same rattle in the front cat as mentioned here.

I have now " emptied " the front cat and all seems fine. I did consider welding a tube inside, but decided to try it first. I can notice a slightly deeper note to the exhaust sound between 1000 and 2000 RPM, but only with no music and the windows open, the new exhaust note is certainly not unpleasant, and with windows closed it is not noticeable at all. I am now planning to change the rear box to a stainless baffled box.

I hope this helps with your descision to do this modification.
 

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oigle

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I did clear the centre cat to remove the blockage as in photos, then I noticed the same rattle in the front cat as mentioned here.

I have now " emptied " the front cat and all seems fine. I did consider welding a tube inside, but decided to try it first. I can notice a slightly deeper note to the exhaust sound between 1000 and 2000 RPM, but only with no music and the windows open, the new exhaust note is certainly not unpleasant, and with windows closed it is not noticeable at all. I am now planning to change the rear box to a stainless baffled box.

I hope this helps with your descision to do this modification.

That CAT sure was badly blocked. Assume you must have had access to good welding and cutting gear and even maybe a lift to do such a job.
 
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stumo

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I'm doing a catectomy on mine as we speak. The front cat is easy to bash out. The rear cat I'm gonna try keyhole surgery. - just cut a small flap in the top side and violate it through that. Then its just a small weld that won't be seen when fitted.
 

oigle

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Be interesting to see how you go by that method. The internals are encased in a heavy gauze type material and is quite hard to break up. You might need a fairly big flap open to do it. I reckon if you cut a U shape and peel it back like some food cans. You could then empty it and fold it back down for welding up. Done on the top wouldn't be obvious. Interesting that the front is easily bashed out - mine is still in place but no doubt will go eventually.
 

Alex Crow

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As above, if you want to be discreet, peel back the top of the housing - would be very difficult through a 'key hole'.
 

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