Looking for crankcase vacuum signal data points

[silver_tt]

I'm measuring about 35" of H20 vacuum signal in my 2014 2.0T and looking for other data points if anyone is kind enough to share.

My car is a 2014 2.0T with 85K miles. I just did the PCV about 2K miles ago with the OE from an Audi dealer. My car burns zero oil between 5K interval oil changes of Driven DI40. I follow service schedules and only use OE parts/erWin specs. I will post my next oil analysis in a few weeks.

[wilmar13]

I used the oil dipstick (or plug) when I was trying to diagnose an oil filter that was crazy tight... I have two data points. My 2011 Q5 2.0 and 2017 Golf R both produced 5cm (2.5") of Hg vacuum at idle when warm which is identical to what you have (35" h2o is ~ 2.5" Hg).

I would like to see what it is under boost, but I only have $14 harbor freight gauge. The PCV valve has so many ways to fail other than the obvious diaphragm, I still wonder if when its under boost, the vacuum at turbo inlet is high, and the check valves in PCV are not stopping it from causing excessive crankcase vacuum, but with diaphragm still intact no excessive oil pass through occurs.

[silver_tt]

Great data points thank you.

When I replaced my PCV recently I did so preemptively. But when I took it out I saw it actually was failing. The little red/organge "button" that I assume is for when the car switches very fast from vacuum pressure to boost was failing in that it was not seated properly (see picture). This was causing oil volatilization to come up through the PCV and was being fed back into the turbo inlet from the hose that goes from that end of the PCV to the turbo inlet. I do my PCV every 40-50K miles.

[wilmar13]

How could you tell it was failing? Is it stuck in an open position in the photo?

[silver_tt]

Yes it wasn’t seated properly and was stuck open. Apparently this is a common failure of this PCV. As you state there are other ways for the PCV to fail beside the diaphragm.

[wilmar13]

OK, I looked at the SSP 606.

Its confusing, I assume that button is what they refer to as the PCV valve (positive crankcase valve valve, haha). See pgs 20-23.
https://www.carworklog.com/stuff/SSP...eneration).pdf

It should be open EXCEPT when under boost (because intake manifold check valve shuts, and there is vacuum from turbo inlet) if my understanding is correct. There is a lot of things to wrap your mind around on this with a lot of moving parts. I really don't fully understand it. It would be helpful to know what normal vacuum is at turbo inlet under boost. I have a suspicion that while oil blow by is the most common (and obvious) failure of the PCV usually due to diaphragm failure, there is some way it can actually create excessive CC vacuum without massive oil blow by, or rather that only happens under max boost and most of us spend little to no time at max boost and high rpm. I just can't figure out any other way my oil filter got so freaking tight.

[silver_tt]

Correct. It's normally shut but when the pressure gets high enough it opens up to reduce the blow-by pressure. In my case, I found it to be not seated properly and I found what I consider to be too much oil in the hose that leads to the turbo inlet -- however, I believe I caught it pretty early because my car burns no oil between oil changes.

Here's a graphic that might help:

[silver_tt]

This is what the new one looks like for reference if it helps as well

[MSq5]

Most reliable way to measure vacuum remains the time-honored mechanical vacuum gauge or in forced induction systems, a mechanical boost/vacuum gauge. It is inexpensive and eliminates the possibility of faulty reading from a sensor.

[silver_tt]

Using a manometer like I showed in post #1 is by far the most accurate and precise way to measure. It measures to .01" H20. This is what professionals use.

[silver_tt]

see time 4:15

https://www.youtube.com/watch?v=i5wW...gQiQ9V&index=8

[MSq5]

see time 4:15

https://www.youtube.com/watch?v=i5wW...gQiQ9V&index=8

Nothing wrong with that, but a simple mechanical vacuum gauge will do the same thing just as well for less. If you have the device, sure use it, but it is not superior for this purpose.

There is no diagnostic or maintenance function on automotive engines that requires or even benefits from the alleged "accuracy" of .01" of water. I doubt any device can attain such true accuracy. It's illusory, like digital calipers being more accurate than those with a dial indicator. They are not.

[silver_tt]

The device is $40, I'm not sure how much less you need it to cost. Not really interested in debating if it's really accurate to .01" (but a simple Google search will show with proof that it is). Crankcase vacuum is extremely important and an accurate and precise device is important in this regard.

[MSq5]

Since you have it, by all means use it. All my shop tools and diagnostic equipment except perhaps RossTech VCDS use mechanical gauges, especially vacuum or pressure gauges. Air conditioning service gauges, vacuum fluid extractors or vacuum coolant fillers, engine compression gauges, cylinder leak down gauges, air compressor gauges and manifold line gauges, etc. I've always validated OBD II sensor reported engine manifold vacuum or boost with mechanical gauges directly plumbed to a vacuum source.

They all work fine. Determining crank case vacuum such as to determine whether a PCV valve is working properly is not rocket science and does not depend on whether the device employs an electronic or digital sensor as opposed to a direct mechanical gauge.

Heck, you can determine if a PCV valve is defective by feel - there will be strong suction at the oil filler cap or the dipstick tube. Typically, there should be a slight vacuum at idle, about 2 inHg no more than 3 inHg. Note, I said inches of mercury, not water. We typically measure automotive vacuum in inches of mercury, boost in psi or hPa. Converting your "about 35" inH2O to inHg, I get 2.6 inHg which is normal at idle measured from the oil cap or dipstick. Taking that number out to hundredths of an inch of water (34.82), even if possible, does not change the 2.6 inHg value materially (34.82/13.6=2.56). No one is going to take it out that far for diagnosis or repair. It makes no sense.

Google is not a reliable source to validate instrument accuracy. It's ok to disagree on preference, but there is simply nothing on an automotive engine that would need even more precision that 1" of H2O, or .1" of Hg.

Here is a good read with the information you seek:

https://www.audizine.com/forum/showt...-PCV-bad/page2

[silver_tt]

We are in agreement that if you don't have a manometer or don't want to buy one for some reason but already have a mechanical gauge on hand then you can use that as an approximation. But the test is more to accurately/precisely measure over time -- especially for me since I just replaced my PCV. I'm just interested in higher precision/accuracy since the cost is so small and the importance of crankcase vacuum is so large. For example, improper crankcase vacuum can cause ring seal to suffer, oil consumption, and all sorts of other fun surprises.

[silver_tt]

Saw your updated notes in your post. We can just agree to disagree about the manometer -- there is a reason professionals use a manometer and not a pressure gauge but like you said it's ok to disagree. I realize that most people aren't as into testing and rigor as I am, again not a problem.

Thanks for the link you provided. I had actually seen that before and it is good information. I agree with "Old Guy" that the PCV should be replaced every ~50K miles and I will monitor the vacuum every 5K at my oil change since it only takes a minute. I also agree with him that it is very foolish to only replace the diaphragm and not the PCV itself -- many people don't seem to understand that there are several other modes of failure possible (such as the one I showed above). Given the importance of the PCV and the fact that the OE only costs $150, it seems very foolish to try to cut corners in this regard.

[MSq5]

Saw your updated notes in your post. We can just agree to disagree about the manometer -- there is a reason professionals use a manometer and not a pressure gauge but like you said it's ok to disagree. I realize that most people aren't as into testing and rigor as I am, again not a problem.

Thanks for the link you provided. I had actually seen that before and it is good information. I agree with "Old Guy" that the PCV should be replaced every ~50K miles and I will monitor the vacuum every 5K at my oil change since it only takes a minute. I also agree with him that it is very foolish to only replace the diaphragm and not the PCV itself -- many people don't seem to understand that there are several other modes of failure possible (such as the one I showed above). Given the importance of the PCV and the fact that the OE only costs $150, it seems very foolish to try to cut corners in this regard.

Professionals are not likely to be using "manometers" or anything except manual gauges for automotive engine diagnostics and maintenance. Manual gauges will work for decades after your wanna be Chinese digital device is in a trash bin. Yes, it works now, but its a fantasy world to be chasing hundredths of the wrong value (inH2O versus inHg) that simply do not matter.

I guess you know that the normal variation of crankcase vacuum from one day to the next is far more than the claimed precision of your instrument. You even rounded to 35, which to us is 2.6 inHg. When you check from time to time, you'll see that variation. Don't take that to mean your PCV is failing if it varies between 2.3 to 2.8 or so, even 2.0 to 3.0. A realistic concern would be an increase in crankcase vacuum that drops the vacuum to -3 inHg or greater, or positive pressure at idle. Anything else is likely pure background noise.

Sorry for what may seem tough love. This ain't my first rodeo, and we all have to learn. We've given you the range of normal values at idle. Might not be best for you to focus on micromanaging those numbers, but knock yourself out.

For what it may be worth it to you, I can share my experience with you via PM. You might be surprised.

[silver_tt]

You're welcome to PM me, always glad to chat with people with interesting data.

Like I said we can disagree about the manometer. I'm not looking to impress you but I've been racing and working on Porsche 911's (both NA and TT) since 2000 when I got out of college. This ain't my first rodeo either.

Ever heard of Tony Callas?
https://www.youtube.com/watch?v=wVLuC84OL5c

Like I said crankcase vacuum is extremely important especially in DFI cars. We can leave it at that.