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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old February 13th, 2008, 12:47   #1
gschwenk
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Default Mystery intake flapper valve?

Well I have the front of the engine torn apart on my newly acquired '97 Passat and in the air intake box is a flapper valve spring loaded closed that runs to a plastic hose running toward the firewall...Anyone know what it does/supposed to do and would it do it better if I surgically removed the valve? In my world the more air the filter sees = lower EGT's and all that.

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Old February 13th, 2008, 12:49   #2
compu_85
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Leave it there. That's part of the warm up system... when the engine bay is cold the airbox draws air from behind the exhaust manifold.

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Old February 13th, 2008, 12:53   #3
gschwenk
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Makes sense, I was surprised how stiff the spring was on it, but if it's connected to the exhaust manifold back there I suppose it would need to be...I imagine it connects post turbo right?? I could go follow it but I'm especially lazy today.
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Old February 13th, 2008, 13:10   #4
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Quote:
Originally Posted by compu_85
That's part of the warm up system... when the engine bay is cold the airbox draws air from behind the exhaust manifold.
Nope. The door is there in case the front snorkle becomes blocked by trash or snow. The door will open if the vacuum in the airbox reaches a certain point.
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Old February 13th, 2008, 13:11   #5
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Oh, oops. Bruce, do the B4 cars have the warm up flapper thing then?
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Old February 13th, 2008, 14:38   #6
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Nope...but the snorkle into the engine compartment is a bit different between the A3 and B4.
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Old February 13th, 2008, 19:02   #7
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Well if that's the case I'm taking that bad boy off of there...I'll get under there tomorrow and see what I see...I really appreciate the input.
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Old February 13th, 2008, 19:46   #8
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Sure. Just be aware that the airbox will be sucking hot engine compartment air rather than cold air as designed. May impact economy and performance.

Now if you close up the hole into the airbox......
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Old February 14th, 2008, 16:42   #9
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So your '97 has a plastic snorkel going back towards the turbo? My '96 has a steel pipe there. Since I live in Puget Sound and seldom drive in the snow, I have removed the pipe from my airbox (makes access to the timing belt WAY easier ). The idea is that if the snowscreen becomes clogged with snow, the increased vacuum inside the airbox will cause the flapper to open, pulling warmed air from around the turbo inside the airbox, and this will eventually melt the snow in the snowscreen.

But I have the snowscreen removed also on mine, so that flapper will never come open unless the air filter becomes plugged (and I have a filterminder to monitor for that).
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Old February 15th, 2008, 10:11   #10
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Geoff, it's not hurting anything to be there, and removing it won't help you get more air into the engine. Why not leave it alone?
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Old February 16th, 2008, 20:48   #11
gschwenk
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Because it's not in my nature to not attempt to improve upon the design of the vehicles under my care.

The tube just stops in the engine compartment, supporting the idea that it's there in case the snorkel get's clogged...It'll be coming out shortly. Weight savings = fuel savings
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Last edited by gschwenk; February 16th, 2008 at 20:51.
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