Beginnings of rough running

Discussion in 'Engine' started by Ade B, Sep 28, 2008.

  1. Ade B

    Ade B Hardcore MB Enthusiast

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    The car is definitely beginning to run less smoothly when cold. This morning, it was making bits of trim resonate when idling in D which is new, and I'm sure I can now hear the engine when cruising at 70ish on the motorway.

    My suspicions are:

    Belt tensioner - I had the belt tensioner shock assembly and serpentine belt replaced when I bought it 16k and 22 months ago, would this deteriorate so quickly?

    Dizzy cap - still on original afaik

    Engine mounts - replaced last Xmas so I'm ruling these out.

    Spark plugs - replaced 12 months ago so should still be good.

    Its not particularly bad and the engine is in all other respects running fine (fuel economy is steady, it pulls strongly etc.) so I'm inclined to leave it until it gets bad enough to reveal the culprit, but it is taking the edge off the car at the moment..

    Its on 67k at the moment and due a B service(?) (the bigger one) soon.

    Any thoughts so I can prepare the fighting fund?

    Ade
     
    Last edited: Sep 28, 2008
  2. Will

    Will MB Club Veteran

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    If the distributor cap has never been changed I'd definately look at replacing that.

    If it's a screw on type I'd be concerned that the fixing screws will be well and truly siezed!

    Will
     
  3. Ian B Walker

    Ian B Walker MB Club Veteran

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    is your 300 cat or non cat?
     
  4. Smiley

    Smiley Hardcore MB Enthusiast

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    did you change the mounting bracket as well as the belt tensioner when you did it? If not then that may be the cause?
     
  5. OP
    OP
    Ade B

    Ade B Hardcore MB Enthusiast

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    Sadly it is with cat... that won't be cheap...:rolleyes:


    I believe so, I kept the bits in the shed, I'll try to dig them out.


    Cheers,

    Ade
     
  6. OP
    OP
    Ade B

    Ade B Hardcore MB Enthusiast

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    Appreciate that a vague "its not running quite quite right" query won't result in a precise answer, but on my list of things to contemplate:

    Disintegrating cat
    Dizzy cap
    Belt tensioner bracket
    MAS/MAF? - Does it have one?
    Vacuum system?
    Injectors?


    Things I've ruled out:

    Engine mounts
    OVP
    Spark Plugs

    Any more thoughts?

    Ade
     
  7. bolide

    bolide Hardcore MB Enthusiast

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    Does it change when the car is in D / P / R?

    I would somewhat suspicious of the gearbox mount

    Nick Froome
    www.w124.co.uk
     
  8. Sp!ke

    Sp!ke Administrator Staff Member

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    Dont rule out the plugs so quickly just because they are 12 months old.

    I 've just solved a misfire by replacing plugs that were younger than that.

    On inspection, there was a lump of crud on the end of one of them :confused:
     
  9. OP
    OP
    Ade B

    Ade B Hardcore MB Enthusiast

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    Yes it grumbles a bit in D at tickover, when I changed the engine mounts we checked the gearbox mount and it seemed to have some flex left and was intact... Sounds like it could be one to eliminate..


    Ade
     
  10. OP
    OP
    Ade B

    Ade B Hardcore MB Enthusiast

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    To bring this to something of a close. Had the car serviced today and fresh oil, plugs and a new air filter have made a clear difference to the cold running. Its much quieter and smoother.. Would never have expected it to make such a difference..

    Would not use Castrol Magnatec again (but then most of you already knew that)..;)


    Ade :)
     

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