Mk4 R32 BFH - Source of fizzing noise on overrun identified - catch can solution?

Discussion in 'VR5, VR6 & Wx' started by G60Dub, Apr 16, 2018.

  1. G60Dub

    G60Dub Forum Member

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    Okay - need some thoughts on this. I have discovered the source of my nemesis fizzing on the overun that I've literally been chasing for 4 years... Yes 4 years! I've had all sorts of ideas from leaky manifolds to leaky injector o-rings... Been through the vacuum system, repeatedly, new gaskets, O-rings etc. all to no avail until yesterday.

    On the MK4 Golf R32 (BFH) there is a small vacuum line connecting the charcoal breather hose and the crankcase breather hose all located just behind and to the left of the throttle body. While it's 100% conjecture on my part (and I'd prefer to know the actual function) I'm guessing this is a pressure bleeding/equalization line of sorts to protect the MAF from blowby gasses or IM from excessive vacuum or an emissions thing e.g. To prevent the drawing of oil down the valve stem seals?

    Anyway I replaced this hose last week with some silicon vac hose - I was out at the car yesterday and noticed the line was noisy... ah...so, I thought I had a cracked union but, yet again, after investigating concluded that the connectors were fine. However, the noise was generated by high air velocity through the line at engine idle - pinching the line at the upstream crankcase end silenced all the noise so no leaks downstream.

    So this got me thinking regarding my 'exhaust fizzing' on the overrun that I've been chasing for years without nailing - How noisy could that vac line actually get if the air velocity upped significantly by the vacuum increasing in the IM? So one quick jaunt indoors and back out to the car with a bulldog clip and nipped the line off and went for a quick drive... Oh lordy me! No horrible loud fizzy leaky noise on the overrun... finally at last! Total silence!

    So now that I've finally found the source of this awful horrid annoying noise what do I do to sort it? I cant imagine a stock car making this noise so why does my vehicle exhibit this frustrating behavior?

    In all seriousness I can only put it down to green Unicorns playing harpsichords and dancing at the spring equinox whilst my back was turned. However, it seems this is not just an issue for me - There a lots of reports of similar frustrating behavior with no cause identified nor a solution for that matter. I don't want to be killing unicorns and would rather fix the issue properly - seems bizarre to me that this would occur without some other hardware having failed.
     
    Last edited: Apr 17, 2018
  2. G60Dub

    G60Dub Forum Member

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  3. MUSHY 16V

    MUSHY 16V Moderator Staff Member Moderator

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    The corrugated bit of that vac pipe split on mine about 3 to 4 years ago
    Only spotted it was split when I put my hand on it and the noise stopped
     
  4. MUSHY 16V

    MUSHY 16V Moderator Staff Member Moderator

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    See the small hole on the cam cover do you have vac leak there ?
     
  5. MUSHY 16V

    MUSHY 16V Moderator Staff Member Moderator

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    The diaphragm can split inside the cover
     
  6. G60Dub

    G60Dub Forum Member

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    Hi Mushy - Its a MK4 so no vortex/cyclonic separator in the rocker cover.

    I've been back out to it and checked it all over and had it all apart, again lol 100% no leaks and the t-piece on the vacuum canister line mounted just to the right of the hard lines (when looking from the front of the car) is simply generating a lot of noise with the airflow through it - I gave it a clean out thinking it may just be gunked up with blowby contamination but no joy.
    I'll have a look at what I can replace it with to see if I can solve the noise issue. At least I finally know that I'm not chasing an elusive leak in the inlet or exhaust system :thumbup:
     
    Last edited: Apr 17, 2018
  7. MUSHY 16V

    MUSHY 16V Moderator Staff Member Moderator

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    Has yours got the little non return valve?
     
  8. G60Dub

    G60Dub Forum Member

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    Hi Mushy

    Its the small reducing tee shown in the attached image thats the noisy culprit. My flapper port on the IM is unused and blocked off at the moment as all that gubbins has been removed - I'm going to try routing this vac line straight to the flapper port using a small silicon elbow and a barbed reducer and then block off the T to see if that helps dampen the noise.
     

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  9. MUSHY 16V

    MUSHY 16V Moderator Staff Member Moderator

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    Mine's is much simplified to this
    The breather going to the manifold and the vac line goes direct from the manifold to the tank under the manifold
     
  10. G60Dub

    G60Dub Forum Member

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    Mine is a fair bit simpler as well - All my SAI plumbing, wiring and vac lines were stripped out a couple of years ago which also thankfully gives a little extra room to work with on the front of the block.
     
  11. G60Dub

    G60Dub Forum Member

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    Decided that given the fizzing noise on the overrun is extremely annoying that I'm considering replacing the stock PCV system with a catch can or similar. Additionally the car has eaten 3 MAFs in 75,000 miles which I can only guess is partly due to fouling from blowby.

    I have an old broken PCV hose so can reuse the connectors from that to attach to the stock locations so no need to butcher a perfectly good PCV hose.

    I've never looked at this in detail before and was considering using something like a Mann Provent oil separator (size TBD). However ideally I'd prefer not to vent back into the inlet system and vent to atmosphere instead - Id happily periodically empty the system so not planning on returning a drain line to the sump. So, what are the pros and cons of each method and if im venting to atmos do I require the investment in something like a Provent?

    This is new territory for me so be kind. :)
     
  12. G60Dub

    G60Dub Forum Member

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    After having investigated this on and off for the last couple of years I've decided to avoid an attempt at simplifying the existing Mk4 breather system also with the addition of a Provent 200 catch can. Basically no matter how I look at it I cannot get this potential solution looking OE neat and the noise generated by the MK4 T piece takeoff just drives me crazy and as such it simply has to go.

    Hence, I am now investigating the possibility of moving to the MK5 breather system where the block blowby is routed via the integrated rocker cover PCV straight into the IM. It looks neat and tidy and as best as I can tell it require the following parts, most of which I already posses;

    MK5 oil burner (plus new Oring if unit is used).
    Mk5 cam cover.
    PCV diaphragm upgrade/replacement.
    New cam cover gasket.

    Now here's where my OCD becomes a real issue;
    The MK4 TB hose has the evaporator connection and I simply hate the idea of messing around trying to plugging this off given the MK1 TT has a similar TB hose but tidier as it doesn't posses said connection. So using this would addtionally force the use of the upper TT airbox and larger MAF meaning updates to MAF scaling tables in the ECU & whatever associated data needs adjusted to suit.

    Eddie care to comment if this is as simple as it appears on the surface?
     
    Last edited: May 19, 2020
  13. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    You can try to simplify the look. But the engineering is well sound stock.
    Same cam cover on the G0lf 4 Motion, Sharan, Galaxy and Mk4 R32.
    Never noticed any noises on either.
     
  14. G60Dub

    G60Dub Forum Member

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    Wish I had pointed it out to you when you were up. I'll take a video and post it up... It really is very noisy and is extremely conspicuous and sounds like a massive vacuum leak on the overrun... Which it isn't!
     
  15. Toyotec

    Toyotec CGTI Committee - Happy helper at large Admin

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    Hardware fault most likely. Not an excuse to fit aftermarket tat...LOL
     
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  16. G60Dub

    G60Dub Forum Member

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    Well extremely noisy it is with no vacuum leaks. The entire section of vacuum pipe passively resonates at a ridiculously loud volume irrespective of material... Eg OEM overbraided line or silicon... Fizzes it's nuts off regardless... Clearly related to the air velocity thru the T piece on the charcoal pipe... Cleaned the t piece out before in the hope there was some lodged detritus partially blocking it but no dice. It's clearly audible at idle and far more intense on overrun. Pinch it and the noise vanishes and confirmed multiple times that there are no leaks in the vicinity hence my want to remove the lot and fit the MK5 breather system. It's driving me nuts!
     

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