high vacuum

[paulperrie]

hi there,
i'm struggling to find out what's wrong with my car.
its a 2006 a4 2.0 tfsi quattro avant with engine code BWE.
the problem i'm having is there appears to be too much vacuum in the rocker cover. the car has started to have a lumpy idle and is throwing the code for too lean at idle. every now and then when at a junction then idle starts creeping up to around 1200 rpm but it doesn't do it all the time. this started me thinking why is the fault intermittent. i've taken off the oil cap when the car has been running fine and there is a slight vacuum in the rocker cover which is to be expected, and i've also tried when the car has been idling badly and you need 2 hands to lift the oil cap because the vacuum is so strong which i think is why its running lean, it's drawing air in from the rocker cover
i have a fair idea of how the tfsi engine works and have checked the N80 valve, replaced the PCV valve , lambda sensor and diverter valve.
i've spoken to 3 different audi garages and they tell me that that engine shouldn't have a strong vacuum in the rocker cover.

any ides would be appreciated.

[a8 tech]

blocked engine breather, disconnect the breather pipe (number 1) and the crank case breather rate.

blank the inlet manifold off and let the engine breather vent to atmosphere and check the rocker vacuum again

http://farm6.static.flickr.com/5014/5465578625_97405d8afb.jpg (http://www.flickr.com/photos/33525279@N04/5465578625/)
A17-10103 (http://www.flickr.com/photos/33525279@N04/5465578625/) by , on Flickr

suggest the problem is either the breather blocked or the manifold tumblers are sticking, either way if disconnecting the pipe reduces the vacuum then its in this area

[paulperrie]

when you say engine breather do you mean the PCV valve?

[a8 tech]

check number 15 and double check pcv for the flap sticking

[paulperrie]

thanks, even though the Pcv valve is new it's worth checking to see that it is working correctly

[a8 tech]

yes just to eliminate it, just suck pipe and make sure the flap opens/closes

[paulperrie]

should the flap be open on high vacuum or boost?

[a8 tech]

not sure Paul, I would need to check that

[paulperrie]

i've got a feeling that when the car is at idle the vacuum in the inlet manifold would be highest because the throttle is almost closed, if the PCV valve was shut then i wouldn't get this high vacuum reading in the rocker cover. if it was stuck open then the full vacuum from the engine would go to the rocker cover which is what could be happening. it would have to be closed when the turbo is fully spinning as to prevent boost from entering the rocker cover

[a8 tech]

sounds good to me

[paulperrie]

took the pcv valve off to check it, seems to be ok the one way check valve is working, there's a spring and diaphram in the valve not sure what that does. the car's idle was perfect yesterday until the evening when it started hunting again. this problem is driving me crazy!!!!!

[a8 tech]

pm sent

The crankcase breather system

The constant vacuum in the crankcase is assured
by a separate breather system for crankcase and
cylinder head.

The blow-by gases emerging from the crankcase
are passed via the primary oil separator in the oil
filter module to the cylinder head cover.

When this happens, the blow-by gases are
mixed with those from the cylinder head and are
passed through a labyrinth, where further oil
separation occurs.

Since turbo operation requires more complicated
pressure control, there is a two-stage pressure
relief valve on the cylinder head cover, which
channels the blow-by gases to the intake
manifold or turbocharger.

When there is vacuum
in the intake manifold, the blow-by gases are fed
directly to the intake manifold.
In the case of charge pressure, a non-return
valve closes in the pressure relief valve housing.
The blow-by gases are fed to the turbocharger
via a channel in the cylinder head cover.

To recognize an incorrectly installed pressure relief
valve, a so-called diagnosis port has been
integrated.

Incorrect installation forces
unmetered air via the sealing area of the
pressure relief valve into the cylinder head cover.

The reaction of the lambda probe results in
diagnosis of the unmetered air and a fault is then
stored in the memory.


http://farm6.static.flickr.com/5217/5486346349_8fdd4ca500.jpg (http://www.flickr.com/photos/33525279@N04/5486346349/)
Capture (http://www.flickr.com/photos/33525279@N04/5486346349/) by

[paulperrie]

thanks for that, i took off the valve again, put it on and fingers crossed the engine light has been off for a week.

[a8 tech]

Any joy

[paulperrie]

no joy, car was at audi on monday the 21st. they reckon the vacuum is ok. they replaced the fuel filter as it doesn't have a set mileage to be replaced, cleared the codes and test drove it. they couldn't fault the car so i drove it and neither could i for about a hour, then the high idle started, then the engine light came on. i'm replacing the N80 valve this weekend incase it's not sealing all the time, and if that doesn't work the next step is to clamp off the hose from the N80 to the charcoal filter anycase the hose is damaged in the wheel arch and drawing in air.
if the N80 valve only operates at idle and when the engine is hot this could be where the problem lies

[paulperrie]

car fixed, turns out it the N80 valve was faulty. this was causing all sorts of vacuum related problems. the car was drawing air from the fuel tank,through the activated charcoal filter and into the inlet manifold, that's why the car was running lean. something i should have noticed was that the fuel tank was creaking and knocking when i used to switch the car off. the tank was collapsing because of the vacuum generated by this faulty valve. the noise has stopped now:Blush:

[a8 tech]

well done that makes sense acf (n80) is integral to emissions hence lambdas going mad trying to correct the mixture and pinging the light on