Crankcase Ventilation Flow Diagram

[A80Avant]

I will disagree with one thing only, that even on a properly working engine, oil vapours WILL make the maf dirty no matter what you do. There are do many threads and posts in this forum about the poor working maf that improved following a good clean with brake cleaners that I cannot dismiss.

Furthermore, I have an impression that on the any/adu if the pressure regulating valve is SJT, there is no way for vapours to go to the one way valve. I'm on my mobile now so I cannot easily see the above photos but I will take some from my car to see if my impression is right

[Billman]

Q: How are then these catch tanks connected when the fumes are not guided to the turbo/maf? The PVC valve does not open then? Do you think the turbo can suck so hard in order to open the valve? I think that something like this would be possible only in the air filter was not letting any air come in so the suction on the PVC would be great to let it open....not sure though

[UrS4boy]

I have no idea what "SJT" means. I know "FUBAR" but not "SJT".

I am not saying the MAF doesn't get dirty sometimes. However, I am saying that I *think* it is impossible for oil vapours to get to the MAF IF the crankcase ventilation components are operating correctly. Therefore, I would suggest that if someone has a very dirty MAF, they should check to see that their bleeder valve and pressure control/regulating valve are functioning properly.

[A80Avant]

Sorry for the SJT, it was meant to say shut, but my fingers are a bit bigger for a touch screen phone .

I like your attitude though, still focusing on a tree and missing the forest...

[newsh]

When the throttle is closed after accelerating, the DV opens and compressed air from the inlet tract is directed back to the MAF tube and turbo inlet. This volume of compressed air expands as the MAF tube is open to atmosphere through the air filter. So if the air is loaded with oil fumes then some of these will make it back through the MAF to the airfilter.

[A80Avant]

I agree with that newsh, but you do know that the oem pcv system tubes are filled with oil gunk and believe me I have had all parts new and cleaned and still had oil there. I cannot believe that merely running higher boost can cause this.

Still, I do not understand the workings of the pressure regulating valve, as o said if it is closed under boost then I cannot see any other way for vapours to move from the block or cyl head to the maf to turbo hose. I will verify this with photos, or apologise if I am missing a hose or tube of some sort.

[UrS4boy]

Who said the pressure regulating valve is closed under boost? It is open.

[UrS4boy]

When the throttle is closed after accelerating, the DV opens and compressed air from the inlet tract is directed back to the MAF tube and turbo inlet. This volume of compressed air expands as the MAF tube is open to atmosphere through the air filter. So if the air is loaded with oil fumes then some of these will make it back through the MAF to the airfilter.

Maybe

http://forums.quattroworld.com/s4s6/msgs/20994.phtml

[UrS4boy]

Q: How are then these catch tanks connected when the fumes are not guided to the turbo/maf? The PVC valve does not open then? Do you think the turbo can suck so hard in order to open the valve? I think that something like this would be possible only in the air filter was not letting any air come in so the suction on the PVC would be great to let it open....not sure though

I am not going to use the word "PVC" because it is vague and does not tell us which valve you are talking about, the "bleeder valve" or the "pressure regulating/control valve". You have to remember that it both of these valves failed closed, there would be a build up of pressure in the crankcase due to blow-by around the piston rings. As a result, even with the connection to the MAF to turbo hose disconnected and redirected to a catch can, at some point there will be enough pressure build up in the crankcase under higher revs (read higher engine load and maybe even boost) that the pressure regulating valve will open (remember that under those conditions, the bleeder valve will be closed) and vapour flow will go to the catch can under a slight pressure.

When the system is connected to the MAF to turbo hose, under the non-engine vacuum conditions, the pressure regulating valve opens mostly due to vacuum due to Bernoulli's Venturi effect of high flow at the MAF to turbo hose connection causing a low pressure area at the opening, like an eductor.

[newsh]

And that diagram doesn't tell the whole story does it, because between the turbo and the throttle body you have the crossmember, intercooler and inlet tube, all full of compressed air

A lot less on the AAN which is vastly superior in this respect..

Maybe

http://forums.quattroworld.com/s4s6/msgs/20994.phtml

[Jamo]

BTW there are uprated one valves available for the audi eurojet used to sell it, don't know if it's still available though

[UrS4boy]

And that diagram doesn't tell the whole story does it, because between the turbo and the throttle body you have the crossmember, intercooler and inlet tube, all full of compressed air A lot less on the AAN which is vastly superior in this respect..

Sorry that most if not all of my diagrams are AAN-related. Does this newly labeled one help at all?

[terrybullwon]

flow from turbo hot side to throttle ?

[UrS4boy]

Quote:
flow from turbo hot side to throttle ?

Who said that? I hope it wasn't me!!?

[terrybullwon]

Who said that? I hope it wasn't me!!?

Its on the diagram