MOT emissions fail after secondary cat delete

Discussion in 'General Discussion' started by BTB 500, Jul 9, 2013.

  1. BTB 500

    BTB 500 MB Club Veteran

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    Just had my R129 fail the MOT on emissions after the secondary cat delete I had done in April. Car has done under 700 miles since the previous MOT, which was fine.

    Luckily I'd put it in early just in case - I've got till the end of the month to get it sorted.

    I've not heard of anyone else having this problem?

    Just to be clear, it failed solely on the emission readings. Not the fact that it only had 2 cats now rather than 4.
     
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  2. IanA2

    IanA2 MB Enthusiast

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    Was it nice and warm before the test?
     
  3. OP
    OP
    BTB 500

    BTB 500 MB Club Veteran

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    How can you control that?
     
  4. C240Sport97

    C240Sport97 MB Enthusiast

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    your title suggests otherwise ..
     
  5. Pontoneer

    Pontoneer Hardcore MB Enthusiast

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    I think he means the engine fully warmed up rather than the weather ?
     
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  6. OP
    OP
    BTB 500

    BTB 500 MB Club Veteran

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    Think you have misunderstood my point.

    It's previously been suggested that reducing the number of cats could result in a fail, even if the emissions were unaffected. That's not the case here.
     
  7. IanA2

    IanA2 MB Enthusiast

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    My MOT place runs an appointments system and it's pretty much drive in and get tested. A good run before that makes sure it's nice and warm.
     
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  8. OP
    OP
    BTB 500

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    I understood that, but what I meant was ... don't MOT stations follow a set process that involves running the car for a certain length of time?
     
  9. IanA2

    IanA2 MB Enthusiast

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    Not sure, but it would seem sensible that it's tested at operational temperatures.
     
  10. OP
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    BTB 500

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    That's what I assumed, but maybe not and your approach is what's needed. Car is in for service and MOT and was dropped off at 7 this morning.
     
  11. Rashman

    Rashman MB Enthusiast

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    Hey Bill.

    Could it be that your primary cats are getting old and could do with being replaced? (I.e, not doing their job as effectively anymore).

    That may be why it failed the emissions test, and not because the secondary cats were needed to pass the test.
     
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  12. SavMan

    SavMan Authorised Forum Sponsor

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    Do you know how much above the limit the car was, if its minor then arranging a set time and taking a long motorway run before arriving will help. It is also worth having your O2 sensors looked at if they are ageing they will also impact the readings and finally there is also the primary cats although they do seem to last quite well.
     
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  13. OP
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    BTB 500

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    Car has done under 53k miles so I would hope the primaries and sensors were OK.

    Haven't got the ticket with the actual readings yet. I will see if I can get them to re-test it hot.
     
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  14. OP
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    BTB 500

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    OK they are going to get it thoroughly warmed up after the service and re-test the emissions - fingers crossed!
     
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  15. Sp!ke

    Sp!ke Administrator

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    Was this a main dealer trying to sell you an entire new exhaust system I wonder?
     
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  16. stereophoney

    stereophoney Active Member

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    The last MOT I had was for my MGF. It was in the garage for over a week and whilst it was there I decided to get the MOT done as I was looking to sell. It failed on emissions. Next day I went the long way round back to the MOT centre having done nothing to the car. A good drive with lots of revs getting everything as hot as it could be. Got to the centre and the car was on the emissions test within 5 mins. Passed without issue.
     
  17. moonloops

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    chuck in a bottle of cataclean and go for a long blast - works wonders.
     
  18. OP
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    BTB 500

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    OK mystery solved, I think.

    The 'secondary' cats that were removed were in fact the only cats. Checking the EPC seems to confirm there is no primary/secondary setup on this car:

    [​IMG]

    No wonder it isn't meeting the emissions test ...
     
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  19. C43AMG

    C43AMG MB Enthusiast

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    I wonder why it passed the first time ?
     
  20. moonloops

    moonloops MB Enthusiast

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    A properly tuned (and mainly modern) engine can pass emissions test.
     

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