Excessive vacuum in valve cover - **RESOLVED**

[lloydy123]

Hi folks,
 
I have excessive engine vacuum in my 2008 2.0 TFSI with 190,000 miles (Ive had it since 3 years old). I have read hours of forums on this one!
I first became aware of an issue when it threw up the CEL, code P0171 - lean burn bank 1.  The car drives perfectly, pulls very well etc, idles normally, no blue smoke or excess oil consumption.
I checked for vacuum leaks and found a split hose at the brake vacuum pump which I have now sorted. There are no leaks remaining.
Problem is that there remains to be HUGE vacuum on the engine. It is impossible to remove the oil filler cap while the engine is running. To be able to remove it I have to break the vacuum by removing the dipstick and then struggle with 2 hands to remove the filler cap. Also  since repairing the vacuum leak when I switch the engine off I can hear oil gurgling from within the engine which occurs until the vacuum is dissipated. I replaced the PCV valve in the hope of resolving the vacuum issue, even though the existing valve appeared to be working normally.
 
Does anybody know why i could have such a huge vacuum? I'm concerned that oil may be vacuuming to where it should not be and hence the gurgling!
 
Many thanks


Update- problem resolved, see page 3

[GVK]

Have read about internal failure of the valve cover causing similar issues but thats all I know.

[ROH ECHT]

The N80 may not be opening. If stuck closed, engine vacuum could be higher and it would run leaner because it counts on the fuel vapors when running.

It could be a throttle or runner flap issue. If those are closed when they should not be can raise vacuum. Are you attempting to loosen the filler cap when you cold start it when runner flaps may be closed? Is it different when warmed?

Also, the PCV diaphragm may not be opening or routing vapors properly to the intake manifold when in vacuum. If you decide to try replacing the PCV...use the same type or last revision for the type you have. There are two different designs and revisions for those two.

[lloydy123]

Have read about internal failure of the valve cover causing similar issues but thats all I know.

Interesting, I've had a read about that just now, seems to be more related to oil consumption problems than vacuum problems, seems a v bad design!

[lloydy123]

The N80 may not be opening. If stuck closed, engine vacuum could be higher and it would run leaner because it counts on the fuel vapors when running.

It could be a throttle or runner flap issue. If those are closed when they should not be can raise vacuum. Are you attempting to loosen the filler cap when you cold start it when runner flaps may be closed? Is it different when warmed?

Also, the PCV diaphragm may not be opening or routing vapors properly to the intake manifold when in vacuum. If you decide to try replacing the PCV...use the same type or last revision for the type you have. There are two different designs and revisions for those two.

I know that the N80 was closed when I checked it with the engine running while warm.

The filler cap is almost impossible to open when the engine is both cold and warm.

I replaced the original PCV, which had a torn diaphragm, about 2 years ago, unfortunately I disposed the original one. The replacement was a random aftermarket one, then I replaced that again last week with a febi bilstein one. From what I had read the PCV changed in late 2006 where the non return valve for the rear brother was moved from the PCV to the rear breather pipe.

I've ordered a vacuum tester and if that shows a high value then I will order up a genuine PCV valve as it must be that which is causing the excess vacuum. If that doesn't work then I'll change the N80 valve. I really hope it isn't a runner flap issue as the car isn't worth much at such high miles, but i'll keep you updated

[ROH ECHT]

But did you electrically test the N80 (supply power) to be sure it opens?

Alright, so with the PCV...there is one for a valved rear breather tube and one for an open rear breather tube. So you should disconnect the short hose between the rocker cover and rear tube to discover which you have so you match it properly with the correct PCV.

If you see a check valve where circled as in the pic...rear tube should be open and the correct PCV pn is 06F 129 101 R:


This is the open or non-valved rear tube:


If you see no valve where circled...the rear tube should be valved and the correct PCV pn is 06F 129 101 P:


This is the valved rear tube:

[pudding]

I thought 06F 129 101 R can work with both the open and valved rear pipes?

I remember fitting revision P along with the valved rear pipe (otherwise you get a high rpm pulsing idle) which was fine, but have since fitted a revision R and not seen a change in engine behaviour.   So do I need to switch back to P?

Bloody confusing all this PCV nonsense 

[ROH ECHT]

I thought 06F 129 101 R can work with both the open and valved rear pipes?

I remember fitting revision P along with the valved rear pipe (otherwise you get a high rpm pulsing idle) which was fine, but have since fitted a revision R and not seen a change in engine behaviour.   So do I need to switch back to P?

Bloody confusing all this PCV nonsense 

Yes...Revision R will work with both rear tubes. You just have two recycle valves to be concerned with. It is more important which rear breather tube is installed and that a Revision P isn't used with the open rear tube.

[pudding]

Gotcha, thanks Ron 

[lloydy123]

But did you electrically test the N80 (supply power) to be sure it opens?

Alright, so with the PCV...there is one for a valved rear breather tube and one for an open rear breather tube. So you should disconnect the short hose between the rocker cover and rear tube to discover which you have so you match it properly with the correct PCV.

If you see a check valve where circled as in the pic...rear tube should be open and the correct PCV pn is 06F 129 101 R:


This is the open or non-valved rear tube:


If you see no valve where circled...the rear tube should be valved and the correct PCV pn is 06F 129 101 P:


This is the valved rear tube:

Thanks for this. I've checked and my rear breather tube is open and my PCV has a valve, so this should be the correct setup.

My vacuum gauge finally came and it reads  a vacuum of 16 inches Hg and very steady, at idle when cold. Is this correct?

[ROH ECHT]

Yep, sounds like the vent-tube and PCV pairing is correct.

Did you test intake manifold vacuum?

My intake shows vacuum to usually be at 18 to 20 inHg when it first starts and it is throttled by the TB and flaps...but shortly thereafter it goes to 21 to 22 inHg. From what I have seen, most see the same numbers on a boost gauge. So your gauge is actually showing less vacuum than mine does on the boost gauge.

Can you do something for me? I am suspicious of the PCV not opening at idle into the intake manifold. With it not running, disconnect the "corrugated PCV to intake manifold tube" from the intake manifold. Wipe the oil from it and (pardon me) suck on it to see if it is open or if it feels plugged. It should be open and then closed when you blow into it.

[lloydy123]

Sorry I should have said that was measured at the dipstick port

[ROH ECHT]

Right, good. Thanks for confirming this. The reason why I asked is because I know what is normal in the manifold and if the PCV is open, then the engine should reflect the same and this might point to the PCV not being fully open to the manifold via the PCV.

It might be worth it to try another PCV...but you can do the test I asked for before. I am just not sure if you applying suction on the disconnected tube can reproduce the vacuum needed to test the PCV valves and diaphragm. So a trial replacement may be needed. If a new PCV doesn't fix the issue...you can swap them around again and hold on to the new PCV for when needed.

I will continue researching this...I wish another had more insight on this topic. I am trying to find out more about something I saw that was pointing a finger at the oil level and oil pump. Can you make sure there is max oil on the Dip's x-hatched marking? How long has it been since the oil filter was replaced?

Just didn't want to drop that concern on you without seeing if the PCV is the problem or not. So let's get the PCV sorted first.

[lloydy123]

Thanks for your help. I have found a split in the the end of my brake booster vacuum line just before the one way valve, this is likely lowering the vacuum. Taping it worked temporarily but now it is getting worse.

I have to confess that my car is an Octavia VRS but I use this forum as there is a great knowledge base of the 2.0 TFSI engine! Apparently the part for this is no longer available from skoda and the aftermarket part from Vaico is not available either. Is anybody able to direct me to the right hose that I can cut to length? All vacuum hoses that I can see online specifically say not to be used for the brake booster line!

IMG_0640 by L Pat, on Flickr

IMG_0856 by L Pat, on Flickr

I still have to perform your check of the PCV diaphragm although I replaced the PCV and both operated in the same manner.

I changed the oil and filter a few weeks ago, always changed at 10k intervals. It sits at the max line and burns oil slowly, about 1.5 litres between services.

[mjmallia]

Buy a new one way valve that the hose is connected to from TPS or dealer, and that is attached to it with the new one

You will also need a sealing cap, due to the new valves having an additional nipple that is not used......mine was green from TPS

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