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Thread: S4 losing boost

  1. #1
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    S4 losing boost

    Hello everybody.

    My S4 is poorly. I posted a few weeks ago saying that I thought one of my DV valves was dead due to the noise it was making when coming off the throttle.
    It now seems to be struggling to boost past 3000 rpm and the noise from the DV (or other air leak) is getting louder.
    It is booked in next Saturday at MRC in Banbury for a health check so the car covers going on and the keys are getting put away until then.

    Do you think it will be ok tho drive it up there carefully? Its all motorway for me so could stick it in 6th and just drive it up extremely carefully or do I stick it on the back of a truck?

    Cheers
    2003 S4 Moro Blue Saloon

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  3. #2
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    Call them and see what they say. I think there is something you can disconnect so it won't attempt to boost past a very low pressure, may help preserve things.
    Present: Ice silver B8 S4 s-tronic saloon (standard)
    Past: Agate grey B5 S4 saloon (MRC tuned)
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  4. #3
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    Driving up there off-boost should be fine,.................don't QUOTE me on that though lol

    Yeah, as said, make the phonecall before you take the risk

  5. #4
    cliveh's Avatar
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    Yea, give Doug a call, but I would agree with the above, and the ECU will normally deliver only "safe" levels of boost under certain conditions.

    But the DVs do not have sensors, so unless their ineffective operation results in something else down the line sensing a problem, this is not guaranteed. Easiest job to be sure is to disconnect the MAF.
    S4 B5 saloon, MRC 400+ (450PS), S2 ABY 1995 Coupe, MRC Stage 2, (292PS), S4 B6 avant (stock)
    RS4 B7 phantom black saloon, mint, fully loaded, low mileage - FOR SALE!

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    IIRC you can disconnect the EGT's, that should limit the amount of boost to 0.3bar so even if you do put your foot down you shouldn't create enough boost to do any damage.

    obviously though as stated above, just take it nice and steady, i've no doubt there's loads of people driving around at the moment with knackered DV's but since they're not thrashing them they don't do any damage
    Dave

    "If that's the Turbo Fairy knocking tell Her I'm not in"

  7. #6
    cliveh's Avatar
    quattro in the bones

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    Yea, that would be a safer option, Dave
    S4 B5 saloon, MRC 400+ (450PS), S2 ABY 1995 Coupe, MRC Stage 2, (292PS), S4 B6 avant (stock)
    RS4 B7 phantom black saloon, mint, fully loaded, low mileage - FOR SALE!

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    shineydave's Avatar
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    lol, only problem is i can't remember where the plugs terminate and i'm at my brothers now and my car is at home so i can't look
    Dave

    "If that's the Turbo Fairy knocking tell Her I'm not in"

  9. #8
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    It's not the EGT's, it's the N75 valve you need to disconnect. I had a serious boost leak on mine and Doug diconnected mine so that I could drive it the 150 miiles back to my garage so they could finish the job off properly! It means the wastegate actuators are left fully open by the ECU so that most of the exhaust gas bypasses the turbine, therefore reducing the amount of boost (and more importantly, turbo speed).

    Would still recommend you try and drive off boost. A motorway journey should be ok with your N75 disconnected. It's stopping and starting at traffic lights that will cause you the most trouble.

  10. #9
    satans child's Avatar
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    ???

    egt's and disconect your n75

    just disconect your maf plug and you wont see more than .5 bar

  11. #10
    jcb
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    get a trailer.....

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    Are you saying disconnecting the N75 will not help Satans_child?

    0.5 bar isn't really miles below stock boost anyway is it?

    Rather than be so critical of others advice, perhaps expand a little yourslef if you can help.
    Present: Ice silver B8 S4 s-tronic saloon (standard)
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  13. #12
    satans child's Avatar
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    no im not...
    but i wouldn't want to explain witch one there looking to unplug as most dont know these cars at all..
    and if im right it wouldn't be any different to unpluging the maf??
    i could be wrong please correct me ?
    im sure you will

    im not being critical just realistic..

  14. #13
    Olly_K's Avatar
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    unplugging the MAF wont help, I used to drive my RS4 with it disconnected due to a faulty MAF and it ran better.

    disconnecting the N75 is dodgey, but probably a better option, the best being a trailer

 

 

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