w124 mot fail emissions

Discussion in 'Engine' started by mattc, Dec 3, 2008.

  1. mattc

    mattc Hardcore MB Enthusiast

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    Hi all

    Nats 1993 e280 has just failed MOT on the following.

    exhaust emissions carbon monoxide content after 2nd fast idle excessive.
    exhuast emissions Lambda reading after 2nd fast idle outside specified limits

    oh, and he did not like the front indicator bulbs (thought they were a bit dim) - so new bulbs for them.

    here's the test data

    fast idle test

    CO max 0.2 actual 1.492
    HC max 200 actual 151
    Lambda min 0.97 max 1.03 actual 0.967

    second idle test

    CO 0.2 actual 0.534
    HC max 200 actual 91
    Lambda min 0.970 max 1.03 actual 0.995

    Natural idle tst

    CO max 0.300 actual 0.290



    The car has only be on local journeys round Brum for a few months now - no motorway speeds at all. Like an idiot I did not take it for a long high speed run beforehand which I have heard can "blow out" the gases. But is there something specifically I should be looking to change? As far as I can tell the Cat and Lambda sensor are original (nothing in the extensive service file to indicate it has been changed either).

    I think the exhaust MIGHT be leaking so can this be part of the problem?

    Thoughts please before I simply start swapping parts.

    I should also add as I am moving home by the end of next week the estate is being rpressed into ferrying duties so not really able to leave it with a garage whilst they diagnose the cause.

    matt
     
  2. SilverSaloon

    SilverSaloon MB Club Veteran

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    1994 W124 E300D Estate, 1985 R107 280SL
    take it for an "italian tune up" (thrash and redline it) after adding some of that injector cleaner stuff into the fuel tank.

    Make sure the car is fully warm before the MOT takes place

    Make sure the exchaust is not blowing anywhere.

    Other than that, i cant help
     
  3. MBK

    MBK Hardcore MB Enthusiast

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    I agree with the above, i take mine for a good long drive on the m40 and the down M4 back to west london before mine goes for its MOT passes every time
     
  4. bouncer

    bouncer Hardcore MB Enthusiast

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    Mattc,

    Check list.

    Air leaks before or after or at the oxygen sensor! ( the just out of bottom tolerance lambda reading 0.967)
    Misfires?
    Faulty coolant temp sensor!

    If not, then looking at the readings the oxygen sensor has become "Lazy" This can be seen as the second fast idle test is done the readings are starting to come into line.
    Note the recovery of the Lambda reading to near enough lambda 1
    Note the drop in HC (unburnt fuel) this shows the cat is still working, and also the drop in CO, its dropped by two thirds on the second fast idle test.
    In my opinion new Lambda sensor will sort this out.
    Not being driven a lot will do this to lambda/oxygen sensors.

    Hope this helps


    sTeVe
     
  5. OP
    OP
    mattc

    mattc Hardcore MB Enthusiast

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    cheers for the replies guys.

    I will change the lambda sensor and take it for a bloody good blast (though not tomorrow as it looks like weather will be ghastly.)

    Should I get a MB sensor or an aftermarket one? Is the aftermarket one a false economy?

    I will report back in a few days
     
  6. BlackC55

    BlackC55 Authorised Forum Sponsor Authorised Forum Sponsor

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    Get a Bosch sensor. ECP do them.
     
  7. OP
    OP
    mattc

    mattc Hardcore MB Enthusiast

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    just looking at ECP site and they seem to have Walker and React parts only for 280's
     
  8. kth286

    kth286 Hardcore MB Enthusiast

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    Get the original Mercedes one, and also get spark plugs from Merc - only about £12 per set.

    But watch the bending of the wiring loom when changing plugs.
     
  9. Redline

    Redline Member

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    Dunno if you have petrol stations with E85 over there, but if you do, running about 50/50 with regular unleaded works pretty good as well. So if you fill it up with E85 and injector cleaner and then go for a good warm up drive I think it'll go straight through! ;)
     

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