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2.4 quattro A6 has hard brake pedal and very rough idle + smoke, any help please?

Discussion in 'A6/S6/Allroad forum (C5 Chassis)' started by shufti, May 30, 2013.

  1. shufti
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    shufti Member

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    [May 30, 2013]
    I've had 6 months trouble free driving from my 2002 a6 2.4 quattro, I used it yesterday and it was absolutely fine. I just went out and started it and it started ok but the brake pedal was hard to push. I drove a few metres to test and the brakes again which were very hard and then the engine idle also become very rough, after trying to rev it it stalled. It then was a very lumpy start after a few tries with smoke from the exhaust, usually it's on the button and never misses a beat

    Has anyone any idea what has gone wrong to cause these 2 problems simultaneously? I'm hoping the 2 things are related as it seems weird 2 things would go wrong at exactly the same time. Any pointers would be really appreciated

    Thanks
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  3. Chrisw4266
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    Chrisw4266 Member

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    [May 30, 2013]
    Sounds like the vacuum pipe from the inlet manifold to the brake servo is split/broken or disconected. This would give you a hard pedal and may cause the rough running as there is an air leak messing up the air/fuel ratio. This is a petrol A6 right? If so check the pipe in may be brittle if the car is old.
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  4. shufti
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    shufti Member

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    [May 30, 2013]
    hi, thanks for the reply

    Yes it's a v6 petrol

    Is the brake servo positioned on the right hand side near the abs pump?
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  5. Chrisw4266
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    Chrisw4266 Member

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    [May 30, 2013]
    It's the round part bolted to the master cylinder for the brakes with the fluid reservoir on top not sure how the petrol is layed out someone else will be along who knows it a bit better. The pipe will be a hard plastic type not rubber.
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  6. shufti
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    shufti Member

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    [May 30, 2013]
    thanks, I'll remove some engine covers and take a look
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  7. shufti
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    shufti Member

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    [May 30, 2013]
    ok I think I found the source of the problem

    I realised the servo what you mentioned was towards the rear close to the battery, I removed the cover and found the full rear bay to be in about 4" of water! Thankfully not reaching the ecu but all the brake servo etc was covered. I've syphoned most of it out and started the car again and the problem is still there. I will let it dry out overnight and tomorrow get it completely dry and also unblock any drain holes so this doesn't happen again

    I'll report back tomorrow as to if any change but if not what sort of damage could the water cause around the related components?

    thanks
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  8. mrnice
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    mrnice Member

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    [May 31, 2013]
    Try doing a search for 'plenum chamber flooding', you should find some good info.
    There are two drain holes, 1 under the battery tray and 1 almost under the brake servo.
    they have stupidly designed rubber grommets in them which get clogged with debris and allow
    water to collect. You have to get to them and unblock them and/or cut them down/throw them away.
    The water can corrode the body of the brake servo and also enter the car through the pollen filter housing amongst other places. When it enters the car it tends to settle under the carpet where a lot of wiring and unfortunately expensive control units are.
    The carpet is inches thick so it's best to take up a corner in the front passenger footwell and feel around under it to check for moisture.

    This problem can get expensive quickly so I'd check these things out asap,
    best of luck
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  9. shufti
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    shufti Member

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    [May 31, 2013]
    hi, yes I've experienced that type of flood before on another a6 I have. That one the front passenger footwell become damp but no more than 2" of water in the plenem chamber, this one is different as the water was at least 4" and there's no cabin water penetration. There must also be an overflow blocked or something to keep the water in the engine......

    OK, the chamber is now dry and unblocked. I started the car and at first the idle was really lumpy but after 10 mins the idle improved. I took it for a drive and it seemed fine with no brake pedal issues or juddering ride but there was loads of exhaust smoke. On lifting the bonnet after the drive there was noticable smoke from the right side of the engine and also a smell

    I'm glad it's now driving ok and some issues seemed to have dried out but I'm worried about this smoke. Is there any suggestions to what has happened to cause the exhaust and engine smoke?

    cheers guys
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