Excessive crankcase vacuum

This is a companion post to my earlier AOS replacement post. My 2010, 987.2 Cayman has excessive crankcase vacuum of approximately -48" H20 as measured by a manometer at the oil fill cap . I replaced the AOS and the issue got worse. I ran a smoke test and wasn't able to find any leaks, loose fittings, or broken vent tubes. What else could cause this high vacuum condition? It is possible that my new AOS is also bad, but that seems unlikely.

Strange, because the problem most experienced is a loss of vacuum, not an increase. For vacuum to exist in any system, there must be intake air and then when put into a closed system of a running engine that pulls air in, vacuum pressure builds and exists at a certain level. Could this be due to a restriction of intake air? Seems like you‘ve checked many areas of the engine for vacuum levels and it remains high wherever you check. Just a stab in the dark, but maybe removing the air filter and checking vacuum levels may yield different readings. If not, then you can eliminate that as a variable in the system. Or else there may be a restriction somewhere else in your intake air. I’ve even heard bizarre instances where someone has found an old shop rag that got sucked into the plenum when a mechanic was working, unbeknownst, and closed everything up, only to be found at a later time. Not suggesting this is your case but strange things do happen. Finding the problem is the bigger issue. Curious as to what you find. Edit: Another thought here along the lines of intake air. Not having a degree in ’Airflow Engineering’, if there is such a thing, could an object have been pulled into the intake vent such as a plastic bag, paper, etc., and be present in the baffle leading to the air filter box, restricting airflow and causing the increase in vacuum? Wild guess, but worth looking into.

Did you replace it with a Porsche AOS or one of the aftermarket ones? I have heard reports that the URO aftermarket one has been known to be bad out of the box. The price difference is considerable (4x?), but taking into account the labor to swap one out - doing it once and only once makes spending more on the replacement unit much more palatable.

It's a genuine Porsche unit.

Update: I ordered another AOS to replace the replacement and it yielded about 25" H20 of vacuum, a significant improvement from the first replacement. That's still higher than spec, but I let the car idle for 10-15 minutes and the vacuum dropped down to 15". I'm not sure if there's a valve that opens at a specific engine temp or something, but I'm going to continue to monitor. I did swap back in the original unit, which I believed was/is failed, and it yielded a similar 25" of vacuum, but never dropped down to 15". Edit: I was wrong about the vacuum dropping to 15". I accidentally switched the units.

There may be a possibility it has to do with this part, and there may be a different part for the other bank. Some time ago I was concerned about positive pressure in the crankcase, (apparently not,) and came across this: https://www.sunsetporscheparts.com/oem-parts/porsche-engine-crankcase-vent-valve-9a110503801

I think that's the part that is included with the FCP euro kit. There's one on each bank. As far as I can tell they aren't "valves" at all, but rather just ports. I can't see any mechanism that would open or close to influence vacuum.

I read somewhere that they do have some sort of mechanism which rarely fails, but if it occurs, it's in a closed position. That said, unless there's some counterintuitive interaction with the AOS, it would cause positive pressure/less vacuum.

@Schmidty Is your conclusion that the replacement AOS was faulty or that the car just needed to be driven a bit for everything to even out? I replaced the AOS with a genuine Porsche unit on my 987.2 yesterday and upon startup, the hose running to the trunk oil fill port collapsed, suggesting excessive crank case vacuum (I don’t yet a have a manometer to get an exact reading). I did let it idle for about ten minutes to get the water temperature up, but it never returned to its normal shape. I’m trying to figure out why a brand new AOS would allow such a high crankcase vacuum.

Unfortunately, I still don't have a resolution. I think the first AOS I tried was faulty, but the second is still giving me excessive vacuum assuming that 15" H2O is the correct until. My vacuum is reading about 25" H2O, but that does correspond to almost exactly 15 oz/in2 so I'm a little concerned that sources online may have units mixed up. I brought it by a local indie and he basically said that the vacuum does seem high, but that I should get a check engine light if there's an issue. He's doing a little more research. Have you discovered anything since your post?