giddyupp

The car is finally running really well. Next project I am considering us the intake refresh. I removed the side plenums at the weekend to see if I could see any obvious issues. Everything seems to be there but all the vacuum and electrical lines do not appear to be routed correctly and it is clear that someone has been in there before. Plenty of electrical tape and mismatched vacuum tubing. So I think Im going to jump in. I did notice a couple of other things that do not look right. Pics attached.

1) What is this and should it come apart like this.


2) Bottom line of the 4 way splitter is plugged - Is this correct ? If not what should this be attached too this.

FredR

The first pic is the eductor that passes metered inlet air directly to the plenum. This device causes a vacuum to be pulled on the servo and passive vacuum system at all times even with the throttle open. Edit- yes it does come out sometimes- not sure if it is supposed to though- I sealed mine with some silicon RTV.

The 4 way splitter allows vacuum from the servo to be sent to the vacuum reservoir and the HVAC system. On the S4 it would also be sent to the flappy but then you have a S3 correct? Thus blanked presumably.

Rgds

Fred

Cosmo Kramer

From the pics, the first one supplies either the brake booster with vacuum or is part of the crankcase ventilation system (probably the latter), second one either supplies the HVAC head or the cruise control.

giddyupp

Should the piece in the first picture come apart like that though ?

hwyengr

The piece in the first pic is commonly referred to as the 'venturi', though much debate has been had as to whether it is technically a venturi. But yes, it does come apart easily (well, at least mine did...)

FredR

For those that know what a venturi is there is no debate. An eductor is a piece of kit that works on the engineering principle of a venturi. In simple terms a fluid is accelerated through a nozzle of reduced diameter and as the velocity increases there is a localised reduction in pressure at the point known as the "vena contracta". The stream being educted is introduced at that point so that it gets sucked in as it were. Then as the localised higher velocity reduces uniformally across the full diameter the pressure increases once more [Bernouilli's principle].

Rgds

Fred

zekgb

On my S3 there are two lines that go from the check valve to the reservoir in the fenderwell and one line to the cabin HVAC manifold. It looks like your picture is correct - what probably happened is that the 4 way splitter was dropped in but then could not be made to reach the plastic vacuum lines coming from the fenderwell so another splitter was added and the extra blocked off on the 4 way. You can clean things up a bit by replacing the 4 way with a 3 way or running new plastic lines from the reservoir of the appropriate length to the 4 way and ditching the extra splitter. It's also a good time to check to see if you have good vacuum on the line going to the HVAC, get out your Mityvac and start testing.

As for the venturi valve they all do that (come apart that is) - on my car I've never been able to pinpoint a vacuum leak from there.

Randy V

Make sure the one-way vacuum valve is installed in the correct orientation.

Brian'sIris

Hi all,

That venturi piece is coming apart easily because the o-ring (your finger is pointing at it in the picture) has developed a compression set and is no longer elastic. The elasticity of a new o-ring will help hold it together better, as well as seal. The o-ring size is 3/8" inner diameter by 3/32" cross-section diameter (dash no. 110).

Please Don't bother using any RTV sealant, for the sake of future repairs. O-ring seals are designed to be used on their own. A light coat of Dow Corning 111 (or similar silicone-based grease) applied to the o-ring will ease installation and keep it soft (elastic) for longer. I could share the story of how difficult my oil pump was to remove due to somebody using sealant (looked like Loctite 574) around the body...again, the only requirement there is the o-ring and a little lube.

Cheers,
Brian

FredR

Kevin,

Spot on- mine came out 5 years ago and no immediate prospect of a replacement thus the RTV. 10 seconds to put a light smear in situ and the repair was done- most of the stuff gets pressed out as you feed the shaft in- just leave it a couple of hours and hey presto. Worked a treat and it will stay that way until if and when it fails.

No idea what a new one would cost but probably the wrong side of $50 if they are available. If one happens to have or can find a replacement o ring that actually fits/works all well and good of course.

Rgds

Fred