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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
Hey. Thanks for the informative post. You describe my symptoms (fuel trim) perfectly.
I have been trying to track down vac leaks on my e46 330i for a few weeks now. I already replaced the valve cover gasket, oil filter housing gasket and both intake boots. All of which were badly perished.

Up until today, I was seeing +28 at idle on the short term fuel trims (but 0 on the long terms.. this confused me, but you say that's expected..). This was triggering the "system too lean" codes.
Thanks to a post on another forum, I discovered that the lower oil separator -> dipstick hose was fractured ( see http://forum.e46fanatics.com/showthread.php?t=773551 ). Mine looked like this:


After replacing this hose today, I am now seeing short term fuel trims hovering around 11 - 14% at idle.

Obviously this is much better, and will not trigger the "system too lean" codes, but I think this means I still have a small vac leak. I guess due to the size of the vac leak that it only affects idle mixture, and actually the car appears to run fine, but I want everything to be as it should be because the car has an LPG (autogas) conversion that is also problematic, but I want to make sure the petrol side is perfect before attempting to fix the autogas side.

I will be buying some starter fluid tomorrow, and I have already checked the air-distributor O-rings, and I have a throttle-body gasket here, but I don't think that is necessary..

Any other ideas where to look for small leaks?

I must say that I can hear intake hiss from the top of the engine (intake mani) roughly around about where the CCV / oil separator is (just forward of the DISA valve). I'm not sure if this is normal for this engine though. I've only had it a month.. I bought it in a bad state :)

The weather is so bad here right now that I doubt I will be able to replace the CCV itself within the next month. Maybe after next month when I have a garage to work from. So any other ideas would be most welcome.

I have a small amount of suction/vacuum from the oil filler hole, and dipstick hole. Nothing very noticable. I haven't actually checked the pressure but I suspect it's nice, and gentle, like it should be, so not a classic case of failed CCV, but I dunno ?

Thanks a million,
Carl
 

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I don't recall to see that kind of hose on the V8. Maybe, on the secondary air pump. I see on your profile that you are driving an E46. This is the E38 section of the forum.....you might want to re-post on the E46 section, or there's even more activity on the E39 side of the house. Maybe you will get a faster answer. Indeed the straight 6 engine has those hoses for the crankcase ventilation system.

QUOTE :

I must say that I can hear intake hiss from the top of the engine (intake mani) roughly around about where the CCV / oil separator is (just forward of the DISA valve).

You are talking about the straight 6 engine for sure....
Yes I am but my post was directed at the OP, since his diagnostics explanation is relavent to my situation (short term fuel trim behaviour, vac leak through the CCV). This is all pretty general BMW stuff, or so it seems (my previous experience is Toyota & GM)

I will be checking the state of a couple of vacuum caps at the weekend anyway, that might cover it.

thanks,
Carl
 

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