Excessive vacuum in valve cover - **RESOLVED**

[lloydy123]

My guess is there is a small crankcase leak somewhere. This could be a leaking seal where anything is connected to the head or block. I have seen a leaky rocker cover seal cause less vacuum at the dipstick. Could be a leaky oil filter housing seal.

Can you replace the dip-stick, remove the IAT sensor, and test intake manifold vacuum?

If the vacuum is more...then it likely has a small leak with something attached to the crankcase (high or low).
 
If you see the same vacuum...then you may need to disconnect the PCV tube from the intake manifold and plug both openings with the gauge toward the manifold. If vacuum stays where it was at the dipstick...then it may be a leak in the manifold itself or in something attached to it.

So the intake manifold pressure is 22inHg when warm which is normal. My understanding is that the crankcase vacuum should only be 1-2inHg if even, is this right? When the car is switched off the dipstick vacuum gradually returns to atmospheric pressure over about 45 seconds which shows that there must not be a big leak anyway.

I checked the n80 and it is clicking well when a power source is applied.

[ROH ECHT]

So the intake manifold pressure is 22inHg when warm which is normal. My understanding is that the crankcase vacuum should only be 1-2inHg if even, is this right? When the car is switched off the dipstick vacuum gradually returns to atmospheric pressure over about 45 seconds which shows that there must not be a big leak anyway.

I checked the n80 and it is clicking well when a power source is applied.

To my understanding, yes. If there is less vacuum in the crankcase than you see in the manifold...then something which is connected to the crankcase's containment bits will have a bit of a leak. Could be rocker cover, oil filter housing, oil pan, vacuum pump, etc..

[lloydy123]

RESOLVED!!

I replaced the PCV valve with one from the dealer and the vacuum has dropped to from 13inHg to 2inHg, just where it should be. Interestingly the 2 aftermarket PCV valves which I had tried both gave different vacuum readings but both were far too high. So do not buy a D2P autoparts or a Febi aftermarket PCV as despite appearing identical to the original and suck/blow testing in an identical way to the original they result in far too high a vacuum!

Thanks to the help of all the folks who contributed.

[ROH ECHT]

Glad this was finally solved. I myself do not trust the quality of aftermarket PCVs...but one day they are all that will be available. Unless, VW sees a good reason not to eliminate them from their stock. Because then this problem would be widespread for their service dept's. I've already seen a number of poor quality PCVs causing leaks of boost when new.

[lloydy123]

Glad this was finally solved. I myself do not trust the quality of aftermarket PCVs...but one day they are all that will be available. Unless, VW sees a good reason not to eliminate them from their stock. Because then this problem would be widespread for their service dept's. I've already seen a number of poor quality PCVs causing leaks of boost when new.

Lesson learned!!

[ILO]

I have a mk5 gti with the same problem as you, i have change pcv 2 times and still i have not fixed the vacum. Do you think a pcv delete will fix my problem? Does anyone what are cons of a pcv delete?