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Discussion Starter · #1 ·
This is my first post, I just wanted to clarify the operation of the ccv valve (this applies to the 5 and 3 series as well.) I've read many posts in the past on how to tell if yours is bad and how to replace, but I thought I might share a little info that will help with vacuum leak diagnostics when the ccv is in fact good. I see the problem quite frequently in my shop.

The ccv valve used in bmw engines works very differently than almost any other design. Most ventilation valves allow a predetermined flow of fresh air through the engine crankcase to prevent acidic vapor buildup from blowby. The amount of air is often dependent on intake manifold vacuum. The ccv on the other hand is designed to ONLY open when there is an ABSENCE of vacuum in the crankcase. The diaphram in the ccv will be fully open upon startup for a brief second until engine vacuum accumulates in the crankcase, at which point the valve will then close. If your crankcase is not completely sealed with a perfect airtight seal at all gaskets, the ccv WILL open and create a vacuum leak. BMW engineers designed the valve to only open to permit blowby to be sucked into the manifold, there is no fresh air/breather intake into the crankcase.

What all this means is that if you have a rough running engine and a known good ccv valve and maf, the first thing you should do is check the short and long term fuel trims. You can use almost any scan tool with live data for this. The combined long and short term fuel trims for our cars should end up somewhere between -3 and +3. Often I will see 02 sensor out of range codes and maf sensor codes on an engine with a rough idle. If you check you will often find a long term fuel trim of 0 (due to the 02 sensors being out of range), and a short term fuel trim of 25 or close to it. 25 indicates the dme is trying to add fuel to a very lean mixture. At 25, the dme is already at its limits as far as trim goes. This often indicates leaking valve cover gaskets creating a vacuum leak which allows the ccv to open when it otherwise shouldn't.

Also don't forget that you can also have leaky gaskets on the intake side that will cause high fuel trim values. A great way to track them down if you see the fuel trim way off is to spray all around the intake manifold and valve covers with starting fluid while the engine is running and listen for changes in the rpm and how the engine runs. A large leak or crushed valve cover gasket will become very apparent. I have even seen new valve cover gaskets that were installed improperly by crushing or twisting the gasket without realizing it. These might even run fine for a while until the leak grows and gets big enough that the dme can no longer compensate for it.

Also, after you replace the failing gasket, make sure you unplug your battery for 10 minutes to reset the long term fuel trims, otherwise it will most likely still run pretty rough and be way too rich. Or if you have carsoft or a gt1, just reset the fuel adaptation values.

Please forgive me if any of this information has already been mentioned by others before. I just wanted to write an article and share my experience. Thanks
 

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Discussion Starter · #3 ·
Nice post Corey. Not to disagree , I do have a question :

Are you trying to say that Is designed to be always open and close when the flow is big through it?

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The opposite actually. The crankcase is sealed. There is no vent to the crankcase for air to enter either metered by the maf or unmetered. The only way air can enter the crankcase is due to blowby or a leaking seal/gasket. If you take your ccv off you can apply vaccum to the manifold port and hold your finger over the port to the crankcase (simulating a good sealed crankcase.) The diaphram will instantly close. Then release your finger from the crankcase port even the slightest bit and the diaphram will open. Very simple actually. No need to worry about metering air or what not. The only thing that should ever cause the ccv to open is blowby gasses, and it does not matter how much the ccv does or doesn't open, because there should be no air for the ccv to suck through besides for the blowby. (This is why perfectly sealed gaskets are so important.)

PS - I have alldata too and did notice the description from them about the pcv. This is generally how a pcv system does work, however not for bmw, which is why i felt i needed to make a post about this as i see a lot of people thinking about it the wrong way. I have been able to solve a ton of driveability issues diagnosing using this philosophy. Many times the customer had been to several other shops and spent hundreds of dollars trying to fix a rough idle or driveability problem with the problem never getting fixed because the others thought the bmw pcv system worked the way it is described in alldata. It does not. Other manufactures do not use the type of system bmw uses because it means one small leak from a valve cover gasket can make a lean mixture. And valve cover gaskets are probably the most common gasket to leak on any brand of vehicle.

Any other questions please ask. Also, I don't know if it is allowed in the forum rules or not, but if anyone needs anything in particular from all data just let me know and i will be happy to post. I have updates through to 2008.

Thanks
 

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Discussion Starter · #7 ·
Ok, I will try to answer in order. Blow by gasses are normally produced all the time but the actual amount of air will be very small. For this reason yes the ccv will be open most of the time. And yes the amount of vacuum in theory will determine how far the ccv will open (at idle it will open less.) However, this is where it differes because it really makes no difference how far the ccv opens or not. It should only have available the blowby gasses to pull through. And in a hypothetical case where an excessive amount of blowby was being produced the ccv would be able to open as far as it needed due to the pressure difference.

If there is a leaking gasket the ccv will already be open. The difference is that the leaking gasket will allow fresh unmetered air to flow through the ccv causing a rough idle. This was the main thing I was trying to point out. Leaking valve cover gasket = vacuum leak. (Very strange thing to see in the design of an engine. Other cars are not like this.)

As for the air pump, on the M62 engines the air pump is only on the vanos engines. The air pump has nothing to do with vacuum leaks or the ccv. The air pump is there to pump air into the exhaust pipes in order to heat up the catalytic converter faster during warm up. (The cat needs to heat up before it starts working.) This is also the reason why bmw automatic transmissions have very late/higher rpm shifts when cold. (To get the cat warmed up.)
 

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Discussion Starter · #8 ·
Just wanted to add that the air pump puts air into the exhaust not to lower temps but to raise them. More oxygen = higher cat temps. (Just like stoking a fire) This is also why cats fail prematurely due to vacuum leaks such as the hypothetical valve cover leak.

Valve cover gasket leak --> unmetered air through ccv --> super lean fuel mixture --> too much oxygen in exhaust due to lack of fuel --> very very hot catalytic coverter, often melting the substrate or at least breaking it apart --> catalyst inefficiency codes and possible restricted exhaust
 

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Discussion Starter · #10 ·
Thank you I'm glad I could help. Also, just to clarify, the metal pipe connecting to the ccv does go to the crankcase. If your engine uses an air pump, which the pre vanos m62 does not, then the air pump will be pulling fresh unmetered air and pushing it into the exhaust manifold, not the head. (the silver disk looking thing sticking up from the exhaust manifold, usually has a vaccum line attached to it)
 

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Discussion Starter · #11 ·
air pump has nothing to do with how the engine will run normally. it is a completely separate system. if there was a fault and the air pump would have to malfunction in 2 ways to affect the engine. the pump would have to turn on, and the port on the ex manifold would have to open. if this happened (very unlikely), then your short term fuel trim might show up as lean, causing more fuel from the dme, causing too rich a fuel mixture and rough idle. this is easily tested though by actuating the valve on the exhaust manifold with a vacuum pump tool.
 
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