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ML 270 Cat Question

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by pace, Oct 16, 2012.

  1. pace

    pace Senior Member

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    Hi all, I had noticed for a few days a smell of exhaust fumes in the car when stopped in traffic. At first I thought it must be the car in front but gradually I realized it was my car.

    On inspection I have found that the 2nd Cat (under the drivers seat) which is shaped like a can has a split forming around the seam. The rest of the exhaust system appears to be in good shape with no corrosion or signs of leakage so this must be a stress fracture?

    Anyway I took the car to my local exhaust man and he has said it can be welded but would have to be removed from the car or could be bypassed with a piece of pipe or could be replaced at a cost of about £300 inc VAT and fitting.

    I am quite keen to remove the cat as I have heard this can improve performance and economy. I would however have to get a piece of pipe made to the correct diameter and shape which could be a problem.

    I am not against replacing the cat as the price is not anywhere near as high as I thought it would be but I would be fitting an aftermarket part which I am not sure about.

    Does anyone have any experience of this particular issue?
     
  2. oigle

    oigle Senior Member

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    Yes. Certainly have. If you put a piece of pipe in, you will get annoying resonance in the system. I did that and had to alter it. Took the pipe out and replaced it with a small resonator (like a little muffler but straight through). Problem 99% solved. Tiny bit of resonance but not enough to annoy. Quite a cheap repair. No discernable improvement in performance with either pipe or resonator. Cat probably would have to be blocked to see a difference when removed.
     
  3. OP
    pace

    pace Senior Member

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    Thanks for that oigle, do you know where I might be able to get the part you describe? or did you make it? I'm in the UK.
     
  4. EmilysDad

    EmilysDad Senior Member

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    I made stainless steel cat replacement pipes for my Senator years ago. I didn't get any resonance with them fitted, but the car was old enough to legally not require them fitted for the MOT. Your car will likely need them fitted to get the emissions right on the MOT.
    Although I've not had the need to replace a cat on a car, from what lads on A N Other forum have experienced, I'd tend to go for a good second hand OE cat rather than use a pattern replacement if need be.
     
    Last edited: Oct 16, 2012
  5. Gkinghorn

    Gkinghorn Senior Member

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    Quite the opposite for me. Removed mine a few months ago. Just took it to an exhaust place , the guy cut them out stuck a cpl of bits of stainless steel pipe in place .. Job done £100 ..zero resonance .... Sounds as it did before but maybe slightly 'throatier' ..but I really don't notice it at all....

    There is a thread on here about all of this but don't listen to Whitenemesis who says we are all doomed if we do this... :p
     
  6. OP
    pace

    pace Senior Member

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    From what I can gather, the car has two cats, one before this one so I should be able to remove it without any problems at MOT time. What do you think the issue would be with an after market cat?
     
  7. OP
    pace

    pace Senior Member

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    I have just had a look on ebay and there are loads of cats for the 270 ranging from £67 to over £400. are any of these worth a go?
     
  8. Gkinghorn

    Gkinghorn Senior Member

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    Pace ..search the forum for "decat"'..... Lots of info ...read them all..

    I went here to get mine done.. http://www.longlife.co.uk/
     
  9. oigle

    oigle Senior Member

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    Every system is different. The ML, with its 3" stainless DOES resonate at 1500rpm quite annoyingly with just a piece of pipe inserted.
     
  10. Gkinghorn

    Gkinghorn Senior Member

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    My mot gets done in a week or so....fingers crossed ppl
     
  11. oigle

    oigle Senior Member

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    The part I mentioned was a standard unit supplied by an exhaust shop. The cost to me in Oz was $80 fitted. Just ask them to fit a resonator in place of the CAT.
    As it is a secondary cat, you won't have issues with MOT. We cannot remove primary cats here but secondary ones are OK to remove.
    If you "pipe" it, you will regret it. Resonance at 1500 revs is bad and that is just where the revs sit when cruising along in traffic at 35mph. Drop it down a gear and no noise. Just at that rev point. I tried to get used to it for a few weeks but finally gave in and put the resonator in.
     
  12. EmilysDad

    EmilysDad Senior Member

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    You boasting? :rolleyes::rolleyes:
     
  13. oigle

    oigle Senior Member

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    Not really....just trying to make the point that every system is different and what works for one.....
    I only very recently went through just this exercise so do know what works with ML270 system.
     
  14. richardN2O

    richardN2O Senior Member

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    I've done the De-CAT, got the T-Shirt and MOT. Search for De-CAT you'll find loads of info and what works as well as dispelling some myths :)
     
  15. OP
    pace

    pace Senior Member

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    How about a piece of flexible pipe?
     
  16. oigle

    oigle Senior Member

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    No idea. The CAT works as a quite effective muffler and taking it out will cause noise issues with this vehicle.
    Flexipipe is different but I think you would still get the same resonance in the system. AUS$80 is only about 50 quid - why not do it right and know you won't have issues? I wasted $50 putting pipe in and had to re-do the job.
     
  17. OP
    pace

    pace Senior Member

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    Fitting a 'resonator' sounds like a good plan. I am not trying to penny pinch but I'm worried that the cat might split right open so I need to get it sorted asap as I use the car every day. I will make some inquiries tomorrow but I just don't know who to ask for a resonator as everyone will be trying to sell me a new cat.
     
  18. oigle

    oigle Senior Member

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    Here in OZ, any exhaust shop would do the job. Not sure about UK. Imagine same would apply.
     
  19. OP
    pace

    pace Senior Member

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    Unfortunately here in the UK people don't tend to be quite so helpful. Most wont want to get involved with a modification and would rather over charge you for a new cat because you drive a Merc!
     
  20. OP
    pace

    pace Senior Member

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    The guy I spoke to said it would be difficult to fit a piece of pipe because of the odd angles at which the pipe enters and leaves the cat.
     

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