Excessive crankcase vacuum

[gcpogcpo]

Hi,

I am hoping a couple of readers can help me out!

My 3.0TFSI (Supercharged) engine has a high level of vacuum in the crankcase. This is noticeable when you remove the oil cap as it is difficult to remove whilst the engine is running. It requires a force of about 2 to 4 lbs to open it.

I also had a PCV fault code and I understand that this combined with the excessive vacuum are signs of a faulty PCV system.

I had the PCV valve and PCV pressure control solenoid replaced by the dealer. The fault code has gone but I still experience the high vacuum pressure in the crankcase. According to my dealer this high crankcase vacuum is normal.

Does anyone else have some info on if this is how it is supposed to be? It will be a huge help if some readers can check their own 3.0TFSI motors to see if you also experience abnormally high vacuum in the crankcase at idle?

As I understand it there is only supposed to be a very slight vacuum just to scavenge any possible blowby air at idle.

Any help will be appreciated! Thanks.

[djn876]

Did they replace with a newer version of the part? I thought there was some recoding to be done in that case but don't know if that would cause your issue or not.

[Morritse]

I only had high crankcase vacuum when I had a bad PCV and it went away when I replaced it

[s4matty]

Im having the same issue in my 2015 with 64k (30k miles)
I put a new oil separator in and pcv solenoid/check valve
It still has very high suction at idle like a shop vac sucking oil cap back down and using lots of oil like 1L every 2 days
Also makes a groaning choppy sound and i pull the dipstick cap the sound goes away
I asked audi if there was update coding for the new oil separator and they said no only for 2010 to 2012.
Im stumped right now
My car is 1.5 months out of warranty so its all out of pocket now.

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[Morritse]

Im having the same issue in my 2015 with 64k (30k miles)
I put a new oil separator in and pcv solenoid/check valve
It still has very high suction at idle like a shop vac sucking oil cap back down and using lots of oil like 1L every 2 days
Also makes a groaning choppy sound and i pull the dipstick cap the sound goes away
I asked audi if there was update coding for the new oil separator and they said no only for 2010 to 2012.
Im stumped right now
My car is 1.5 months out of warranty so its all out of pocket now.

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Don't drive your car like this

[hjaaamjb6]

Same. Brand new latest revision PCV... oil cap still hard as hell to take off..

[Rs4#0198]

The crankcase is under high vacuum to help minimize oil consumption. The higher vacuum helps keep the rings tighter against the cylinder walls which helps with oil consumption. There are different breathers for 3.0 so if a higher vacuum is installed on your engine it needs to match the ECM software.

[s4matty]

Has anyone had recoding done after the updated pcv installed for b8.5?
Im told from my local dealer there is none
But there just a small dealer and dont seem to know much about the 3.0T


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[Jroyalty7]

Has anyone had recoding done after the updated pcv installed for b8.5?
Im told from my local dealer there is none
But there just a small dealer and dont seem to know much about the 3.0T


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Before swapping mine to the upgraded pcv I searched this heavily and called dealerships all across the country... couple people said you need to update the ecu afterwards, others said there is no update necessary. I installed mine over a year ago and have not really run into a noticeable issue...yet lol

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[Waffles_s4]

How do u guys know if there is a bad pcv? Does it leave a code, and how do u know which pcv (are there many)?

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[djn876]

Excessive oil consumption and heavy vacuum when running and trying to remove the oil cap.

[Waffles_s4]

Excessive oil consumption and heavy vacuum when running and trying to remove the oil cap.

Hmm I think mine is hard to remove while car is running, but don't they all do that?

Where is the pcv and how do we bench test it?

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[djn876]

PCV is under the supercharger, needs to be removed for access. I've never tried to remove my oil cap while running but my understanding is that it's not just a little vacuum but unusually difficult to remove. Not sure what other testing can be done with it installed, would have to dig through the shop manual or old threads to see

[Morritse]

How do u guys know if there is a bad pcv? Does it leave a code, and how do u know which pcv (are there many)?

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Bad PCV doesn't lead to heavy oil consumption. Telltale signs are coolant in the oil, lots of white steam in the exhaust, invisible coolant loss

[djn876]

A bad PCV can cause increased oil use. It can also result in leak(s) as the crankcase pressure isn't vented properly. Isn't always use by the engine, but it can certainly be a sign of a bad PCV.

The excessive oil consumption on the early PCV versions was one of the symptoms it was going to bad and there are a few threads here on it.

[Waffles_s4]

PCV is under the supercharger, needs to be removed for access. I've never tried to remove my oil cap while running but my understanding is that it's not just a little vacuum but unusually difficult to remove. Not sure what other testing can be done with it installed, would have to dig through the shop manual or old threads to see

Well my oil cap feels pretty hard to remove, though I don't seem to have oil or coolant loss.

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[hd1]

Just changed my pcv and caps still hard to pull off. I only burn a 3/4 quart every 4-5k. I changed bc MY WP/Tstat bc they were beat (leaking) , and did the carbon cleaning at same time. I think it's normal to a degree. No ecu reset done

[gcpogcpo]

After i queried the vacuum issuse the dealer rechecked the car for any issues including any recoding and indicated none needed to be done. They replaced with the latest version of the part. Mine is a 2013 but don't know if the part installed is a newer revision to what was installed.

As i understand it the solenoid valve was also only added from about the 2013 year so perhaps this change is what is resulting in different experiences being noted re vacuum on the forum.

I have no noticeable adverse effects of the vacuum and no excessive oil consumption. I am just not always sure if the high vacuum could cause damage to crankseals over time and thus cause premature leaking.

[gcpogcpo]

How do u guys know if there is a bad pcv? Does it leave a code, and how do u know which pcv (are there many)?

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Yes mine threw a code. Code is gone after repair job but high suction remains

[gcpogcpo]

Thanks all for your input. Reading the feedback it seems as if a vacuum pressure of some sorts is not abnormal.

Below is an extract from the dealer as to how the system works which they sent to explain why there will be vacuum. The extract notes that the system is designed to reduce the vacuum from 700mbar to approx. 40mbar.

Perhaps it is this part of the system not working properly and as such is not reducing vacuum as much as it should? At the moment we know there is vacuum but don't know how much?

An objective test would be to measure the vacuum to see whether it is in line with the design spec. I have read of some people making a vacuum gauge that is connected to the oil cap and which can then accurately measure the vacuum.

Has anyone else heard of such a device?

Dealer extract :
Crankcase breather system.

It prevents vapours enriched with hydrocarbons
(blow-by gases) reaching the outside atmosphere
from the crankcase. The crankcase breather system
consists of vent ducts in the cylinder block and
cylinder head, the cyclonic oil separator and the
crankcase breather heating.

How it works:
The blow-by gases in the crankcase are drawn in by
the intake manifold vacuum via:
- the vent ducts in the cylinder block,
- the vent ducts in the cylinder head,
- the cyclonic oil separator,
- the pressure limiting valve and
- the crankcase breather heating
and then fed back into the intake manifold.

Cyclonic oil separator
The cyclonic oil separator is in the cylinder head
cover. It has the task of separating oil from the blow-by
gases in the crankcase and feeding it back to the
oil system.
A pressure control valve limits the intake manifold
vacuum from approx. 700mbar to approx. 40mbar.
It prevents the same vacuum forming as in the intake
manifold and thus engine oil being drawn in via the
crankcase breather or seals being damaged.

To purge the crankcase, air is extracted from the clean air line
(downstream of the air filter). The clean air then flows into the
crankcase through a line connection on the fine oil separator.
During the development of the system the following objectives
were pursued:
• Reduction in noise emission
• Improved engine idling performance

To reduce noise, a plastic coil was integrated into the pipe system.
A high hydrocarbon concentration in the crankcase could impair
the engine's idling performance. Idling performance is improved
by the crankcase ventilation shut-off valve N548. This valve closes
the vent line when the engine is idling if the oxygen sensor detects
an excessively high hydrocarbon concentration from the positive
crankcase ventilation system. The crankcase ventilation shut-off
valve N548 is activated by a PWM signal ↗ from the engine control
unit. It is fully open when de-energised ("fail-safe position” )