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W211 MOT Emissions fail - next steps?

Discussion in 'Engine, Drivetrain, Fuel and Exhaust' started by gez, Aug 12, 2019.

  1. gez

    gez Senior Member

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    Your Mercedes:
    W211 E320 CDi Estate, R129 Brabus SL500 (SOLD), R231 SL400 AMG Line
    My 2003 W211 E320CDI with the straight6 648.961 diesel engine has failed it's MOT on emissions.
    The average reading was 1.53 against a plate value of 0.6.
    I changed the air filter, though it didn't look too dirty, and added a bottle of Wynn's "Pre-emission test treatment" to the maximum strength they recommend (30 litres of diesel) and have thrashed it for 100+ miles, making sure it was well warmed up before it's retest.
    However, it failed the retest with an average only down to 0.85.
    I get my cars tested at the council depot so they do not offer repairs.
    The car has just under 100k miles, runs fine, no engine mgmt light etc., is fully serviced and is too good to scrap unless I have no reasonable alternative.
    What are the next recommended steps?
     
  2. Wighty

    Wighty Senior Member

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    Well , that improved massively . Maybe do the same again and if the improvement is the same the car will pass ?
     
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  3. OP
    gez

    gez Senior Member

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    The guy did a second retest for me immediately after the 0.85. That averaged 1.1 so seems to vary.
    I could give it another go if recommended but I'm guessing there's something a bit more long term needed.
     
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  4. LostKiwi

    LostKiwi Senior Member

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    Sounds like it needs to go on Star and look at the live running values - particularly MAF, lambda and injection values.
     
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  5. Tony Dyson

    Tony Dyson Senior Member

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    Has the car been modified at all during it's lifetime?
     
  6. OP
    gez

    gez Senior Member

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    No, nothing modified.
     
  7. Blobcat

    Blobcat Moderator

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    Your Mercedes:
    R171 SLK280 3.0, Land Rover 110 County SW
    No warning lights or limp home? (thinking MAF)
     
  8. OP
    gez

    gez Senior Member

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    Your Mercedes:
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    Nope, no EML, no other warnings or errors, has always run fine.
    It does mostly do short runs with only occasional longer journeys, so that probably doesn't help.
    The guy at the MOT center did say he was surprised that the plate value was only 0.6, but he showed me the sticker to confirm. He said many much newer cars have much higher manufacturers limits - up to 3.2, but clearly he cant change the target!
     
  9. Wighty

    Wighty Senior Member

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    The car may well have fault codes that don't trigger a dash warning light or limp mode . Has the car been "read" ?
    My car had a faulty O2 sensor for ages with nothing on the dash .
     
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  10. Botus

    Botus Senior Member

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    whilst we shouldn't condone running tractors with poor emissions, I expect any other MOT test centre will have no issues at all with it completing an emissions test.

    the only difficulty I can see is if the failures are recorded and a very keen MOT inspector was to follow things up, either way the problem would be with the testers and you'll be on the road....
     
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  11. EmilysDad

    EmilysDad Senior Member

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    like putting the exhaust probe up another car's exhaust ...... :rolleyes::rolleyes:
     
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  12. Wighty

    Wighty Senior Member

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    Oooooo Mrs !:eek::D
     
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  13. V6Matty

    V6Matty Senior Member

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    MOT for my car this year we couldn’t get it to do an emissions test, probe went in but there was so little exhaust gas at tick over it wouldn’t register so wouldn’t start the test.
     
  14. Wighty

    Wighty Senior Member

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    :eek: ! Which car , and what happens next buddy ?
     
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  15. V6Matty

    V6Matty Senior Member

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    This was with the 212, not much happens now, just gets registered in the MOT that a emissions test couldn’t be completed, nothing more than that
     
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  16. Jim2

    Jim2 Senior Member

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    Off, hand, anyone know what are the NOX emission's from the 2010 MB E class w212 with the 2.1 CDI engine?
     
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  17. Gazwould

    Gazwould Senior Member

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    No need , VED is CO2 based and MOT for dervs is simply smoke opacity .
     
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  18. bembo449

    bembo449 Senior Member

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    did you give it an Italian tune up before you took it , I find when I get a customers car that I know is used for short journeys , I make sure I get it hot and give it a bit of stick to clean it out
     
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  19. malcolm210

    malcolm210 Senior Member

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    Try some premium fuel and cetane enhancer (Millers) that might help as already said the car almost passed the second time. It might be that the inlet manifold needs cleaning they do sludge up especially with short runs leading to inlet port shut off butterfly valves in the manifold being stuck
     
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  20. d215yq

    d215yq Senior Member

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    As a last resort (might cause engine damage on a CDi but unlikely for a one off and if you're considering scrapping it anyway for this fail...) you could just chuck in veg oil. Mine was once a borderline fail on opacity (the only test they do here) so just put 5L of veg oil in with a near empty tank for every MOT, and since then has been about 0.5 (before was 2.4, spanish limit 2.5, and only passed at 2.4 because the kind supervisor suggested i rev it to 1500rpm instead of 2500 rpm!) ...and yet I've done nothing to the car inbetween. Very noticeable on start up too how much cleaner the emissions are (you can't actually see/smell them!).

    You could put 5L in to a near empty tank a few miles before the test, and then fill it with diesel immediately after to reduce chance of damage.

    The emissions test is hard here because it's the last test after inching the car through all the others yourself in a queue, so the car has been idling for 45 minutes building up soot before the test is done. Perhaps make sure on the retest they take the car straight to the machine and it's not sat about restarted/idled for a while etc which could allow it to build up stuff after the Italian tuneup?
     
    Last edited: Aug 16, 2019
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