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What now for the AEB?

Discussion in 'A4/S4 forum(B5 Chassis)' started by Lee Goodall, Mar 11, 2009.

  1. Lee Goodall
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    Lee Goodall ..got my head together!

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    After trying to iron out issues with boost control a big problem has come to light!!!

    Pressure testing my boost system has indicated that I have an issue with the cylinder head/valves/valve seals.

    I am getting a large amount of boost leaking back through the cylinder head and exiting through/around the oil filler cap!!

    I presume this is down to one or more faulty valve seals unless anyone can tell me differently?

    What should I do?
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  2. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator

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  3. Lee Goodall
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    Lee Goodall ..got my head together!

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    Forget about this thread for now.. I will update later on.
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  4. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    i think its possible for this to happen thru the breather system?

    Might indicate a faulty 1 way valve or something. The inlet is connected to the breather system and there is a 1 way valve thats supposed to close under boost pressure. Have you plugged/disconnected the PCV line before pressurising the inlet?

    Valve sealing issues wouldnt allow boost pressure into the rocker cover, and would show up in a compression test as low compression on that cylinder.
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  5. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    lol wha?
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  6. Lee Goodall
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    Lee Goodall ..got my head together!

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    For the exact reason you've just stated.. I'm going to investigate later on.
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  7. jcb
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    jcb Active Member

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    think he means "valve seal" as in the noun
    rather than "valve sealing" the verb.

    knackered valve seals and guides would allow boost into the rocker cover....but it would also show up in your exhaust as huge plumes of smoke
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  8. Lee Goodall
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    Lee Goodall ..got my head together!

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    Yeah thankfully no smoke so will hopefully turn out to be an easier fix than I first thought. There's no obvious poor running (other than the boost issue) so I'm guessing there's no compression issue.
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  9. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    aye it sounds like your feeding pressure thru the PCV valve on the turbo intake pipe into the breather system. The 1 way on the breathers T-Piece stops the boost normally getting thru into the crankcase under boost from the inlet, but you've kinda bypassed that by creating boost pressure in the TIP. :p
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  10. Lee Goodall
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    Lee Goodall ..got my head together!

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    Yeah.. needs blocking off at the TIP for boost testing!!. Doh!!

    So no pressure should come through the valve (from breather to TIP) under boost then obviously?
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  11. Lee Goodall
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    Lee Goodall ..got my head together!

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    I thought the PCV vented the cylinder block?.. How does the pressure from the boost test get into the head? I'm confused now.
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  12. andybnwc
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    andybnwc Member

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    you need to block the connection on the y pipe for the pcv , i air is coming through the pcv then 1 or more of the 1 way valves in the spider assy will be bad , you can get the whole spider with the valves and may aswell do the fhose delete while installing
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  13. Broken Byzan
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    Broken Byzan Photographic Moderator Staff Member Moderator

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    The boost tester connects to the TIP which is non pressureised anyway, it is however connected to the PCV system via the pancake valve, so as such when you send pressure through it it feeds direct into the sump, seeps past the rings sometimes. But as Lee has already found the air in the PCV system makes the oil bubble and can be heard through the oil cap .

    The pancake needs to be blocked off so when pressuring through theTIP the air goes through the turbo and then into the pipework inc DV though the FMIC and into the the throttle body. There will be a small seepage past the throttle butterfly but nothing to write home about.
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  14. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    andyb: its a 1.8T not an S4, but the principle is the same.

    Lee: the pressure gets fed to the sump, sump is connected to the head by a number of oil drains which the air simply flows thru and into the rocker cover.

    The Idea is that the crankcase should be under vacuum at all times when the motor is running. In an NA engine you simply connect the inlet manifold to the breather and that does the job, and this connection is still there on an AEB for when its not making any boost. However when it does make boost the inlet is no longer in vacuum, so on an AEB there is a small 1 way valve (sits on the end of the T piece thats connected between the Z pipe and the metal hardline that runs to the pancake valve) which blocks the inlet vacuum supply once it becomes pressurised, and instead uses the pancake valve so the gasses are vented to the turbo inlet pipe, as thats the only place in the system there is still negative pressure.
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  15. Lee Goodall
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    Lee Goodall ..got my head together!

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    Ok that explains it then.. the pressure finds a route to the head from the sump via the oil pipes etc if the PCV isn't blocked off.

    When the system is pressurised 'properly' with the PCV blocked how long should it hold the pressure for at 17 - 18 PSI?
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  16. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    quite a while? i'd expect it to start dropping pretty quickly if there was a leak, accomanied by some hissing...

    Otherwise its just whatever leaks past the rings?
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  17. Lee Goodall
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    Lee Goodall ..got my head together!

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    It held for about 40 - 50 seconds but decreased throughout.. this sound ok? No hissing or obvious leaks anywhere.
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  18. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    i'd have thaught it would have held a little longer? Try it with the throttle body open? as perhaps its just slowly leaking past there into the cylinders? Once the cylinders are full it should hold for much longer i'd think?
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  19. Lee Goodall
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    Lee Goodall ..got my head together!

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    Hmmm yeah to be honest I thought it'd hold for longer but def worth I try with the TB open. As you said maybe the throttle plate is holding some pressure.. Hopefully get another chance to test it soon.
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  20. Lee Goodall
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    Lee Goodall ..got my head together!

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    A pic from last night.. Trying to get the TIP back on the turbo in the dark after I blew it off while testing!! Had to take the headlight out to get to the jubilee clip properly.

    Nearly popped my eardrum when it blew off!

    [​IMG]
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  21. Lee Goodall
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    Lee Goodall ..got my head together!

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    Can anybody compare this with their own pressure test?
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  22. Lee Goodall
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    Lee Goodall ..got my head together!

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    Anyone?? Come on.. somebody on here must have done a boost pressure test on an AEB.
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  23. aragorn
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    aragorn "Stick a V8 in it!" Staff Member Moderator

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    i presume it did the same when testing with the TB open?
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  24. Lee Goodall
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    Lee Goodall ..got my head together!

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    To be honest mate I have had a manic weekend and not had time to test it with the TB open yet. I was hoping somebody would have some previous results though just as a guide.
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