[vespa]

The N55 PCV system is permanently integrated/sealed into the valve cover and is generally non-serviceable but an understanding of the function and fault diagnosis may be useful to some so I will attempt to explain the method of operation. Before you shake your fist at "the man" for "keeping you down" I'll point out that the PCV valve is not only one of the most impactful and significant pollution control devices ever implemented, it also keeps fuel from destroying your oil and is one of the main reasons oil change intervals have gone from 2500 miles in the 1960's to 15,000 miles today.

If your crankshaft front or rear main seal is howling, whistling, squealing, chirping screeching or chattering like this, this, or this, check the PCV valve first. SIB 11 03 11 explains that faulty front and rear crankshaft seals were installed on all models produced between 7/1/2009 and 8/31/2011 but I suspect that many of these seal problems are actually caused/cured by the PCV valve. Photos below detail the failure of the rubber diaphragm in my 05/2011 which led to problems with both the front and rear main seals.

I don't believe there is any design fault with the PCV valve nor any reason to panic over the very high replacement cost or seemingly short life of some. I refer to the valve with "doom" for several reasons:

1. It is easily damaged by improper boost leak testing.
2. It can lead to some shockingly high repair bills. (Front/rear main seals can cost $1000/$2000)
3. It can easily be overlooked as the culprit. (My dealer missed it twice)

Method of operation:

Vapors are drawn from the crankcase thru the top rear left corner of the valve cover and a convoluted molded oil separation passageway is visible leading forward to the prominent round pressure regulator valve at the top-center, inappropriately labeled with an electrocution warning sticker. Separated oil drains back into the head thru some small passages just prior to the regulator.

On the top outside of the PCV regulator valve is a hose barb with a non-sealing decorative cover (squeeze inner sides to remove). A tiny bit of air will flow in/out of this port into a sealed chamber inside the valve whenever it is changing positions but there should never be any continuous flow. The crankcase pressure is intended to be approximately 38 mbar (0.55 psi) below the local atmospheric pressure at all times and this is maintained by a simple passive system consisting of a spring trying to open the valve while outside air pressure (thru the barb) tries to close it. When the valve is open, vacuum is drawn from the intake, and when it is closed pressure builds up from piston blowby gasses. The PCV system is connected to the intake in 2 places: before and after the turbo -- so there is always a source of vacuum available. A simple one-way valve on each of these routes ensures that air can only flow out of the crankcase, never in. The net result is that crankcase pressure generally remains between 0 mbar and -38 mbar under all conditions. Don't take these numbers too seriously though, it's just a simple passive valve.

One of the passages goes direct into the cylinder head with no hose. The head has 6 small passages in the aluminum casting connecting the intake ports directly to a convoluted molded chamber visible along the entire left side of the valve cover. A bulge in this chamber near the PCV regulator contains a simple free-moving one-way valve to prevent turbo boost pressure from entering the system.

The other passage uses the accordion metal hose at the front right of the engine. When the system is under boost there is no vacuum in the manifold so this alternate path is provided to utilize suction from the turbo inlet: Under the square protrusion at the top-front of the valve cover is a second identical one-way valve leading to an flexible metal hose connecting to the intake pipe just ahead of the turbo. Thanks to Bernoulli this junction can become quite cold so a heater is typically included on the hose to prevent ice droplets from hitting the turbo.

Along the entire right side of the valve cover there is a large vacuum tank that is completely unrelated to anything -- this was simply a convenient place to put a tank. The small shiny rigid molded hose running across the top center of the engine connects the chain-driven vacuum pump to this tank, and from here the wastegate and exhaust flap are actuated.

Failure mode:

The one-way valves are quite simple and robust, as is the sealing portion of the regulator valve itself. Clogging, leaking or gumming up of any of these mechanisms appears highly unlikely. But unfortunately the diaphragm actuator has very thin edges that can crack and leak. When this happens the valve will fail to close and the crankcase will be exposed to excessive intake vacuum, likely resulting in front and/or rear main seal squealing and/or damage.

If you have any reason to suspect PCV system malfunction, first open the oil cap to see if the problem (e.g. main seal noise) immediately subsides -- this is perfectly safe and will confirm that crankcase pressure is related to the problem. The engine will stumble a little as it goes lean from the unexpected air flowing thru the crankcase and into the intake manifold without passing the airflow meter. The meter (MAF/TMAP) is deliberately located upstream of all PCV activities so as to eliminate the possibility of oil contamination.

You can easily test the PCV valve for failure by holding a smoke source (match, cigarette) close to the hose barb with the engine idling. If smoke is continuously ingested into the valve the diaphragm is leaking. Alternatively you could check that tissue paper clings to the barb tip, or for absolute certainty you can attach a clear hose and see if motor oil or water is continuously drawn in. More scientifically you could apply 38mbar positive pressure to the barb with the engine off and confirm that the pressure is held for a reasonable time but few shops have the equipment for that. Do not connect a pressure gauge to the barb while the engine is running, you will interfere with the PCV operation and will not get any useful information anyway.

Cause of my valve failure:

The radial direction of the crack in my valve is quite curious and does not seem consistent with fatigue so I suspect it may have been exposed to high pressure and "popped". The system is well designed such that the delicate diaphragm portion of the valve can never be exposed to raw intake vacuum or boost pressure -- only regulated crankcase pressure. And the crankcase pressure can never be too high or too low, thanks to the PCV regulator and related one-way valves. It's pretty foolproof, unless you're a fool.

I only owned the car for 4K miles when this happened so I don't know the history but I think the previous owner must have done one of two things:

1. Connected a pump to the barb and sucked/blew hard enough to pop the valve diaphragm. I can't imagine any reason someone would do this, but I can guarantee it would break the valve. My barb was curiously missing the decorative cover suggesting that someone may have messed with it.
2. Performed a pressure test of the entire intake tract without removing the oil cap. Pressure tests should be performed from the turbo inlet pipe with a kit like this, but if you have an aftermarket intake with some round connection that seems more convenient, you will end up pressurizing the crankcase if you don't remove the oil cap. This occurs because you are pressurizing both PCV vacuum sources (pre/post turbo) so the air that inevitably leaks past the piston rings and PCV one-way valves will slowly pressurize the entire crankcase until the regulator diaphragm pops. It's only designed to handle 0.5psi so hitting it with 20psi or so will surely burst it.
   

Repair procedure:

I detailed the E92 N55 valve cover replacement procedure here:
http://www.e90post.com/forums/showthread.php?p=18946466
Cost is $400.

Some trivia about the "4 cylinder N55", a.k.a N20/N26:

Where the N55 regulates crankcase pressure from both sources, the N20/N26 only regulates when drawing vacuum from the intake manifold -- the pre-turbo pipe is completely unregulated. This seems quite reasonable since the pre-turbo intake seldom has much vacuum, and even when it does, it's only very briefly and at a time when blowby gases are at their peak anyway.

The N55 does not have true Positive Crankcase Ventilation, it literally just sucks. The N20/N26 on the other hand has an extra hose drawing fresh filtered air into the crankcase at all times. The extra flow of ventilation is likely the reason that the N20/N26 has such a large rubber PCV hose on the front of the engine compared to the small metal accordion hose of the N55.

Lastly, One of the key "advances" separating the N26 from the N20 is the new N55-style non-serviceable PCV valve. The literature explains that this is necessary to reduce evaporative emissions and is one of several tweaks that led to the SULEV rating.

[Rob@RBTurbo]

Outstanding information and tutorial! Great information. It is a shame that the unit is not serviceable, however, on the N55.

[Jsoboti]

If the SIB exists for it, should the dealer replace free of charge even if the car is out of warranty?

[ibrian]

Originally Posted by Jsoboti

If the SIB exists for it, should the dealer replace free of charge even if the car is out of warranty?

Hi Jsoboti - did you ever find an answer for this?

Thanks,
Brian

[vespa]

SIBs do not extend the warranty. They simply help the repair shops to correctly diagnose and correct the problem.

[GORDON.M3]

The unit is serviceable but quite a hack job.
https://vanos-bmw.com/membrane-for-b...er-11127570292

[vespa]

Wow! That's crazy! This must be a pretty common problem if they are making repair kits for it. I sure am curious to figure out what is causing this failure.

Has anyone had a PCV failure without either JB4ISO or an improper boost-leak test?

[PhaseP]

This valve is used one way or another in many different BMW engines including NA N52 and seems to be common that by age either cracks or dirt builds up on sealing surface and gives problem.

[AJ9x]

Originally Posted by gordon@

The unit is serviceable but quite a hack job.
https://vanos-bmw.com/membrane-for-b...er-11127570292

Gonna give this a shot within the next week. I will report how it goes when it's finished.

[dannyjones]

This whistling/chirping issue is happening to me since installing a JB4. I cannot reproduce the sound on map 0, but on map 1 and map 4 I can reproduce it (and the JB4 should be doing stock map on stock 4...). I don't know why I don't get the sound without the JB4, and I hope the JB4 isn't what caused the valve to break. I've owned the car for 3 years and I've not done any kind of pressure test. I'd hate to replace the valve cover only for the new one to break as well...

I couldn't identify the problem with smoke, but Vespa kindly helped me out and it appears my PCV valve is blown as well. I think I've verified it with a small tube from the valve and putting it near a small amount of water it sucks it in constantly.

https://www.dropbox.com/s/ccqukqgf02...41.25.mov?dl=0

Hope it can help someone

[AJ9x]

Originally Posted by gordon@

The unit is serviceable but quite a hack job.
https://vanos-bmw.com/membrane-for-b...er-11127570292

http://www.e90post.com/forums/showthread.php?t=1384967

Here's a thread on said hack job. Finished it and it's working fine.

[remixsecret]

Originally Posted by AJ9x

http://www.e90post.com/forums/showthread.php?t=1384967

Here's a thread on said hack job. Finished it and it's working fine.

I did this hacked job with the PCV valve replacement part off vanos website. Squeal is still there but less now, but else could be the issue to fully get rid of the howling sound?

[lwgrenier]

Hi I have a 2011 335, not sure about the build date. I removed the oil cap to see if the chirping noise would go away indicating a problem with the PCV valve. The noise did not subside (thank god) but there was a noticeable suction on the oil cap as I was removing it. Also there was a fairly loud rattling/clinking noise coming out of the oil cap opening. Is this bad? I removed the cap before the engine had warmed up on a ~35 degree day, not sure if that would make a difference.
Thanks!

[vespa]

A lot of suction and terrible metal-on-metal clanking noises are completely normal, believe it or not.

[gillzj00]

Saturday night I pulled into the garage after about a 20 mile drive in some cold weather (30 degrees or so) and took this video:

You can't see much but the sounds are almost identical to the first video mentioned in this post.

I've been driving the the car the last couple days and I don't think it has been making that noise anymore. I will try to blow some smoke near the PCV valve and see it gets sucked in this evening.

My questions are as follows: If am hearing that squealing coming from under the car, is the air being sucked into the engine from one of the main seals, or is it being pushed out of the main seal?

If I am hearing that noise is my seal already shot or if I get this issue fixed soon might I have saved it?

For the PCV diaphragm repair, did you guys just dremmel the old one off, put the new part on and slather JB Weld around the sides while applying pressure? Or did you put a bead of JB weld between the new part and the valvecover before setting the new PCV ontop and applying pressure?

Thanks for any help!

[GORDON.M3]

You can try to repair the PCV first to see if that restores normal operation.
Dremel it off, clean up the area. Centre the new PCV then apply JB weld around it.
Don't put jbweld in the seam as it can get squished on to the rubber diaphragm and cause more problems.

[vespa]

Originally Posted by gillzj00

Saturday night I pulled into the garage after about a 20 mile drive in some cold weather (30 degrees or so) and took this video:

Sounds like the rear main seal and the noise should go away instantly when you remove the oil cap. It's just air whistling past the seal like a party-balloon and is not an indication of damage but it does pull the lubrication out the seal while also increasing the contact pressure so it will cause the seal to wear more rapidly. If that seal wears enough, it will leak a little oil and/or continue to make some noise even after the PCV is fixed.

[gillzj00]

Last night I took a candle out into the garage when I got home. Left the car running and blew it out under the hood near the PCV valve. I didn't see any smoking going into to the valve. It looks like there is a little cap on the end of the barbed PCV valve, do I need to remove that, if I remember right it is kind of clipped on there but moves freely?

The car wasn't squealing at that time but I seem to notice it when I am driving in a parking ramp and slowing down, I can hear a sound reflecting off the wall that sounds like the squeal I was hearing the other night. It only last 2-3 seconds.

I think I read that I could pull the oil cap off and put it back on and that would cause the engine to re-vacuum itself up and that might help me replicate the seal squealing.

I guess my question would be if the PCV valve seems fine, is it possible my rear main is just worn out? Would it be worth replacing the PCV with the new diaphragm as a cheap test?

Also, I have a good friend who is a Mercedes Benz Master Technician, should I ask him to do a smoke test for me or any other more technical diagnostic?

Thanks for all your help and responses guys, I know I am not an e90 guy so thanks for making me feel like family!


Just got home, pulled oil cap off and put back on after 30 seconds or so, no squealing. Pulled following Carly codes and got myself excited with a horror story about the 28A0 and their camshaft bearing caps were expanding and about to fail?? (http://www.bimmerfest.com/forums/sho...d.php?t=977220)

2 codes found:

28A0 - Throttle valve opening angle-intake pipe absolute pressure, comparision pressure too high

2775 - Air mass plausibility: air mass too low.

[Strumnon]

Would installing an oil catch can before an issue develops help prevent a problem ?

[sberendt]

Sorry for bumping this older thread. This was a very informative post! I recently was told to look into the PCV system because I had a strange issue that happened.

In the video linked, I had noticed a slight whining sound when under throttle. It’s pretty subtle and would happen every time I drove. The reason why this is interesting is because 2 days ago I was getting a complimentary oil change done at the dealership and they told me my valve cover gasket was leaking. I had them replace the gasket and cover. Ever since I picked up the car, the sound is now 100% gone... do you think there is any correlation??

Check out my video:

Thank you in advance!

[asquared]

Originally Posted by gillzj00

Last night I took a candle out into the garage when I got home. Left the car running and blew it out under the hood near the PCV valve. I didn't see any smoking going into to the valve. It looks like there is a little cap on the end of the barbed PCV valve, do I need to remove that, if I remember right it is kind of clipped on there but moves freely?

The car wasn't squealing at that time but I seem to notice it when I am driving in a parking ramp and slowing down, I can hear a sound reflecting off the wall that sounds like the squeal I was hearing the other night. It only last 2-3 seconds.

I think I read that I could pull the oil cap off and put it back on and that would cause the engine to re-vacuum itself up and that might help me replicate the seal squealing.

I guess my question would be if the PCV valve seems fine, is it possible my rear main is just worn out? Would it be worth replacing the PCV with the new diaphragm as a cheap test?

Also, I have a good friend who is a Mercedes Benz Master Technician, should I ask him to do a smoke test for me or any other more technical diagnostic?

Thanks for all your help and responses guys, I know I am not an e90 guy so thanks for making me feel like family!


Just got home, pulled oil cap off and put back on after 30 seconds or so, no squealing. Pulled following Carly codes and got myself excited with a horror story about the 28A0 and their camshaft bearing caps were expanding and about to fail?? (http://www.bimmerfest.com/forums/sho...d.php?t=977220)

2 codes found:

28A0 - Throttle valve opening angle-intake pipe absolute pressure, comparision pressure too high

2775 - Air mass plausibility: air mass too low.

Long shot but did you ever get these codes figured out. I'm having the 28A0 code on my N55 X5. Happened pretty much same time my serpentine belt jumped and shredded as I was pulling home. The code triggers manifold pressure sensors, but I'm getting a weird clattering sound also, so wondering if this could all be related to my front crank seal as I noticed there is a significant gap. I inspected carefully and pretty confident no belt got past.

Also wondering if it's related to the PCV valve bc after starting the car for a minute or so and shutting it off, I can see a little bit of smoke creeping up behind my crank pulley. Also smoke comes out when the oil cap is removed, seems way too quick for the motor to smoke like it does after a quick start and stop. Here is a picture of my front seal, looks like it's too far in and has a gap. Just need somebody to confirm whether this is normal or not. Need to know where to start as this is our family car.

Also read about a noise upon braking. I was getting almost like a grinding, squealing noise when I brake at slow speeds. I assumed it was the brakes but my pads still have a lot left on them. Even took the brakes apart a few weeks ago and cleaned them. But the noise never went away. Could that also be related to the front seal? Hoping @vespa can chime in as well.

[gillzj00]

I never did get these codes figured out lol. The issue hasn't gotten worse. The squealing seems to happen more in cold weather but it always goes away a few seconds after it starts. Not really sure what is going on.