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Thread: Boost Leak

  1. #1
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    Boost Leak

    Guys,

    I have developed a major boost leak over the weekend and still havent totally fixed it. On Friday my car would only boost to about 8-9 psi (normaly 15-16 psi) and all I can hear is air gushing from under the bonet and I dont know where its comming from.

    On first inspection I took a few pipes etc off to see what the problem was and noticed a 1 inch split at the turbo end of my turbo intake pipe. I thought great I know what the problem is then ordered one from audi. N.B. forge dont make a silicon one for the AJL engine code.

    Anyway changed the 'TIP' yesterday and although it improved slightly it didnt totaly solve the problem. After the change I was getting 9-10 psi with the same gushing air noise when I try pushing the throttle right down.

    So after that I changed my N75 to the N75J varrient just to see if it was that. It made the car much crisper at the lower rev range (1400 - 2800) and lower boost range (0 - 6 psi) as it did when the car was running fine. However the car now boosts to about 10 - 11 psi but still air is gushing out from somewhere.

    I have checked for visable signs of split pipes all over the engine bay and nothing appears obvious. All clamp connections also seem fine. It sounds like the gushing air maybe comming from round the airbox/turbo side of the engine bay and not the intercooler side, though I cant be 100% sure. With no obvious splits I am thinking along the lines of a faulty valve, though dont know which one.

    Any ideas guys? Its a bloody pain that you cant load the turbo up when the car is stationary because its differcult to check for leaks when driving. So is a proper look on a rollong road the only way to find this? Or you reckon VAG com could give me a better clue?

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  3. #2
    simon_golf_tt's Avatar
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    Re: Boost Leak

    Have you got another DV you could try? Could be that.

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    Re: Boost Leak

    As Simon says, try changing the DV. Also, i would go and purchase a whole set of heavy duty jubilee clips abnd replace all of them from airbox to throttle body as the audi ones really are sh*te. Check the hose from turbo to hard pipe and from hard pipe to intercooler and intercooler to throttle body. If this doesnt solve it, check the intercooler hasnt been punctured or anything (unlikely!!). Can you still hear the air gushing? If not, it could be that the split hose has knackered the MAF...wouldnt be the first i've heard of going like this.

    let us know how you get on.

    Rich

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    Re: Boost Leak

    Cheers guys,

    However if you didnt notice on my sig I have changed my DV to a piston type about a year ago. It maybe that but I doubt it as the piston type are pretty reliable in comparision to the diaphram type.

    I will have to have another more detailed look when I get time around the associated pipework. I did look at the intercooler itself, and didnt notice anything out of place. Also checked the pipes & connections in and out of the intercooler and to the throttle body again nothing obvious. though the pipe from turbo to intercooler was differcult to insepct due to its location so there maybe something hidden down there.

    Its a really loud gush of air so there must be a significant leak somewhere of which I am guessing wont be just a pin hole in one of the pipes. You dont think VAG com will give me any better idea then guys?

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    Re: Boost Leak

    [ QUOTE ]
    Cheers guys,

    However if you didnt notice on my sig I have changed my DV to a piston type about a year ago. It maybe that but I doubt it as the piston type are pretty reliable in comparision to the diaphram type.

    [/ QUOTE ]

    Piston type DV's have been known to stick therefore being half open/closed. Definately something to check!

    [ QUOTE ]
    You dont think VAG com will give me any better idea then guys?

    [/ QUOTE ]

    Probably not... It reallly will only tell you what you already know.

    Rich

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    Re: Boost Leak

    [ QUOTE ]


    Piston type DV's have been known to stick therefore being half open/closed. Definately something to check!

    Rich

    [/ QUOTE ]

    Rich,

    Fair point. I presume if the DV is stuck between settings then this would cause a perminant alternative path/bleed for the air to gush through back into the airbox and hence preventing a build up of boost. I think I will try my old DV back in if I can find it, mind its a t**t of a job on the A4. Not technically differcult by due to it being so low down its bloody awkward and gives you a bit of back ache.

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    Re: Boost Leak

    Mat - don't think Vagcom will tell you about leaks, just requested boost and actual boost. It is possible to pressurise the pipework if you make a bung for one end (throttle body) and a bung with a tyre valve in the other end (turbo outlet) - or vice versa. I have done this before and it does work - then you can hear the leak. It pressurises the whole pipework from the turbo through the intercooler to the inlet manifold. I used a compressor to pump up the pipe work. This is a PITA though and will require a fair bit of time to make all the bits you need. I have seen a proper manufactured bung with valve before - so maybe you can buy them from somewhere (it was for an S2). It needs to be the right diameter for the hose at one end. I just used an old maf body, a bicycle inner tube for the valve, a coffee jar top, some resin and loads of silicon - sounds blue peter ish - but hey it worked! To bung the other end I used a full aerosol can!

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    Re: Boost Leak

    Simon,

    Thanks for the info. Hey nothing wrong with a little innovation, cant fault you for it. I will have a play with the DV first and if that doesnt fix it maybe I will look at pressuring the system somehow. But if I change my mind and cant be arsed with making a blue peter special then I may take it on a rolling road and have a look on there. I must admit I am tending to think along the lines of the DV valve at the moment, so a bit of luck and it will just be that sticking and nothing more serious.

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    Re: Boost Leak

    Well good luck mate and let us know what it turns out to be!

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    Re: Boost Leak

    Apparently taking out the drivers side headlight helps with changing the DV on our cars. Wish I had tried this before scraping all my knuckles to shreds. Also removing the offside lower bumper grille might improve access.

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    Re: Boost Leak

    Guys,

    Due to carring out major work on my house I have only just got round to changing my DV and having a good look at my turbo pipework. Unfortunately I havent solved the problem. But I have ruled out the following:-

    a) DV (changed to new 710N)
    b) N75 (tried orginal & my 'J')
    c) TIP (replaced)
    d) Any of the turbo pipework clamps from all accociated systems including intercooler etc
    e) Any obvious splits/holes on any of the turbo pipework from all accociated systems including intercooler etc
    f) Any obvious holes/damage to intercooler
    g) Fault codes with the engine management system

    So I am buggered if I know what the problem is. I still am thinking its something to do with one of the valves and am now thinking along the lines of a vacuum leak/fault in the system causing problem with either the N75 or DV. Any more ideas woulkd be appreciated guys.

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    Re: Boost Leak

    Cheers Tim,

    thanks for that. You got to let me have a drive of yours when you finaly fit the turbo. I am still in two minds whether to cut my loses and get another car or go all the way with the GT28RS & proper brakes etc. I have spent alot of money on mine (5k ish) and I know I will never see any of that again, plus mine does handle extremely well so am happy with that side of it. Its just the brakes & engine that I always thrive for better performance.

 

 

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