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HELP - why have I lost all boost?

Discussion in 'A4/S4 forum(B5 Chassis)' started by Drizz, Sep 18, 2009.

  1. Drizz
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    Drizz Project Plush

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    [Sep 18, 2009]
    This morning on way to work my car lost all boost. Vacuum is as normal, the bailey dump valve open and closes as it should but I have no positive boost at all? It's a 1.8t btw. Any help much appreciated
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  3. Blue_Thunder
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    Blue_Thunder Active Member

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    [Sep 18, 2009]
    A hose could have popped off. Vacuum would be unaffected by that.
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  4. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 18, 2009]
    Ye it does sound a bit like a hose, or some other boost leak like a split intercooler. If it was ECU or boost control related you'd end up on wastegate actuator pressure which is around 4psi.
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  5. Blue_Thunder
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    Blue_Thunder Active Member

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    [Sep 18, 2009]
    If it was only a split intercooler (or any other kind of minor leak) you would still expect it to reach some boost, that's why i'm thinking of somethign like a major boost leak, ie: hose completely popped off.

    This happened to my S once midway through a spirited drive up in Scotland. It was pretty obvious because as soon as you tried to accelerate hard it was like stomping on the brakes. You could also hear the air rushing out.
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  6. my96A4Turbo
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    my96A4Turbo New Member

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    [Sep 18, 2009]
    happend to me last week,,,,the pipe that runs from the actuator to the inlet had just came right off ( the pipe was hard and brittle& just crumbled away)........
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  7. Oranoco
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    Oranoco Well-Known Member

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    [Sep 18, 2009]
    The actuator rod could have come off the wastegate arm. This means the penny remains in the open position and no positive boost is achieved
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  8. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 18, 2009]
    or the penny valve could be embedded in the cat somewhere :p

    penny valve "fell off" on mine according to the service history, somewhere around 120k miles.
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  9. Drizz
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    Drizz Project Plush

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    [Sep 18, 2009]
    Hmmmm Well ive taken the undertray off and check the hoses and all seems intact. Intercooler looks fine too. No whistling to indicate a boost leak so can only imagine its the turbo area. Ill go and check that inlet to actuator pipe and i doubt i can get to the actuator arm but ill try and check that too.
    Not a happy bunny today :(
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  10. Geeman
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    Geeman Low Life

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    [Sep 18, 2009]
    Could just have gone into limp mode if the turbo's spiked. Have you driven it since you stopped the engine?
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  11. Blue_Thunder
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    Blue_Thunder Active Member

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    [Sep 18, 2009]
    Limp mode and/or actuator failure would still result in wastegate pressure (ie: a bit of boost would still be produced because the turbine is forced to spin until the pressure of the exhaust gases open the wastegate (it remains closed by a spring until this point).

    I suppose it could be something causing the wastegate to remain open, ie: broken wastegate spring.
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  12. Geeman
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    Geeman Low Life

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    [Sep 18, 2009]
    A broken or incorrect MAF can cause similar problems too. I installed the incorrect MAF in mine a while back and it wouldn't run, tried to stall when accelerating, etc...
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  13. Drizz
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    Drizz Project Plush

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    [Sep 18, 2009]
    Right to answer some Q's. Yes ive driven it about 50miles since over 3 journeys. It drives and idles normally, just wont boost. No management light, no noises, just no boost.
    Im thinking as theres no audible difference it wont be boost leak, and no management light means it wont be electric. It must be turbo/actuator....
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  14. Geeman
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    Geeman Low Life

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    [Sep 18, 2009]
    Yeah... a MAF failure would produce a warning light.
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  15. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Sep 18, 2009]
    Drizz you VAGcom'd her yet?
    Maf as a complete fail can produe a MIL,assuming it has one, I can't remember what year your car is AEB ones don't have an engine light

    But MAF lowsignal may not put a light on, as it could be borderline
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  16. Drizz
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    Drizz Project Plush

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    [Sep 18, 2009]
    I dont have VAG com unfortunately.
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  17. Drizz
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    Drizz Project Plush

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    [Sep 18, 2009]
    Will disconnecting the battery remove any fault codes like it does on Vauxhalls? Thinking if i disconnect it, leave it then reconnect and see if it drives ok intially?
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  18. Siena
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    Siena Active Member

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    [Sep 18, 2009]
    I'd be inclined to concentrate on the turbo area...

    Have you removed the intake pipe from the turbo? I'd do so, and check the actual turbine shaft isn't broken. I have a 2000 A6 1,8T, the shaft had snapped in two, so the exhaust turbine was still spinning, but seperate from the compressor turbine.
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  19. Drizz
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    Drizz Project Plush

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    [Sep 19, 2009]
    So take off the airbox to turbo pipe then start it up and see if its turning yeah? Or if its snapped itll fall out anyway?
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  20. Siena
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    Siena Active Member

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    [Sep 19, 2009]
    No, just remove the turbo intake pipe, and check the compressor shaft by hand. You'll soon know if it's still connected to the turbine shaft.
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  21. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 19, 2009]
    The only thing the ECU can do is open the N75 and let the actuator see all the boost. The actuator opens the wastegate at 4psi, so if it was an electronic issue it would give you 4psi...

    MAF etc could cause it, but it'd also show other signs of running ****.

    I suspect its a mechanical issue with the turbo itself. Can you hear any "spool" noises at all?

    I'd either try and get a vagcom scan, or remove the cat/downpipe and check the wastegate.
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  22. Drizz
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    Drizz Project Plush

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    [Sep 20, 2009]
    No un-normal noises at all. Ill be removing intake pipe tuesday and seeing if the shaft is obviously knackered and go from there....
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  23. Drizz
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    Drizz Project Plush

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    [Sep 22, 2009]
    Well the turbo shaft feels normal. Has to be something electric im now thinking as surely the boost guage is -20 off throttle and 0 on throttle. If the turbo wasnt working at all surely it would stay in vacuum? or am i talking nonsense?
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  24. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 22, 2009]
    When our penny valve broke (before we got the car) the initial diag report says 2psi peak boost...

    As i've said, if its electronic the turbo would still run actuator pressure, which is 4psi. The ECU cant force the boost any lower than that.
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  25. Drizz
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    Drizz Project Plush

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    [Sep 22, 2009]
    Must be penny valve then
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  26. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 22, 2009]
    When the penny valve breaks (or the actuator/wastegate jams open) the turbo will still spool, as some of the gas will still flow thru the turbine...

    Hence you will still get a tiny amount of boost.
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  27. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator VCDS Map User

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    [Sep 22, 2009]
    Shouldnt be too hard to check, pop the cat flange bolts and wiggle it back a bit then look in the crack?
    #26
  28. Drizz
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    Drizz Project Plush

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    [Sep 22, 2009]
    ill get it done soon, gonna vag com it first just incase
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  29. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator VCDS Map User

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    [Sep 28, 2009]
    Have you solved it yet Drizz?

    It's exactly the symptoms we now have with the A3
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