Boost leak-strange or not?

[piotr]

Hi .So my car was mapped by Mark(AutoMark)and on that day everything was ok but next day - in every gear it’s boosting and suddenly there is a very Violent boost cut.
I have done leak test as per Mark instructions but there is no external leaks.What I did noticed is that all 2Bar of pressure I pumps in the system will disappear in about 30-40seconds.I can hear that air inside of oil sump and I can hear it when I open oil filler cup .Why is that happening and what should I check?

[mike74]

My bet would be the pcv check valve under the back of the inlet manifold. Less than £10 for the part and prepare yourself to lose valuable knuckle skin changing it!

[newsh]

As above, I had this tiny plastic valve stick open years ago, it blew the valve cover gasket.

Also check your DV diaphragm by pulling the vac hose off the IM and sucking on it, should hold vacuum.

When you did the test, did you disconnect the Z shaped PCV pipe from the MAF hose?

[John.]

My bet would be the pcv check valve under the back of the inlet manifold. Less than £10 for the part and prepare yourself to lose valuable knuckle skin changing it!

Is this the same valve that can make the car smoke from the exhaust for a while after starting from cold?......

[piotr]

My bet would be the pcv check valve under the back of the inlet manifold. Less than £10 for the part and prepare yourself to lose valuable knuckle skin changing it!

Good shout.Can you still get them valves as new part.Any chance for PN?Many thanks

[Colesy]

The MAF has caused boost cuts like this for me, just unplugging and plugging back in used to fix it.

[piotr]

As above, I had this tiny plastic valve stick open years ago, it blew the valve cover gasket.

Also check your DV diaphragm by pulling the vac hose off the IM and sucking on it, should hold vacuum.

When you did the test, did you disconnect the Z shaped PCV pipe from the MAF hose?

Hi buddy,DV shoud not be a problem as i have replaced with new one,also i have installed the Saab one that sould be stronger then Audi unit and still the same problem persists.When i did boost leak test i did it the same way as when i was with Mark(Automark) so disconnected hose from turbo and charged all system that way.No i didnt disconnected Z shape PCV pipe and to be honest im not sure which one is it?
Also i have noticed oil leak from back of the rocker cover from the half moon (its all new gaskets/seals) so it is probably result of pressure escaping there.I wonder if there is a way of blocking this valve just for the purpose of test?

[piotr]

The MAF has caused boost cuts like this for me, just unplugging and plugging back in used to fix it.

I will try this but connections are clean and MAF is brand new .

[mike74]

have a search for p/n 035103245A on ebay...theres loads on there at around £7 a pop

[piotr]

have a search for p/n 035103245A on ebay...theres loads on there at around £7 a pop

Diamond

[newsh]

To avoid pressurising the crank case you have to disconnect the PCV system, this is done by disconnecting at the engine side of the MAF hose, the pipe that goes to the cam cover. Plug the MAF hose with a 20mm bung and do the test again.

The PCV Valve is hidden in the join of two pipes under the back of the IM near the throttle.
One end is 24mm and the other is 13. I turned up a “dummy” one out of solid ali when I was tracking leaks on the RS4. You could just remove it and plug both sides, no harm will come to anything. My coupe has none of this stuff and just runs a catch can vented to atmosphere.

[newsh]

The valve

[piotr]

Perfect info-thank you for that.I will do the test after new year as im going for holiday and will let you know the outcome.
Happy Christmas ta all forum members and familys.

[newsh]

Happy Christmas mate
Have a great time.

[mcandmar]

It can also leak past the turbo seals and make that bubbling sound, in which case leak test from the turbo output hose.