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Old 01-12-2014, 05:22 AM   #1
MINIz guy
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Default M44 PCV help

I posted over at Bimmerforums but nobody has helped me yet.

I've noticed that I am getting more leaks as the weather is getting colder. I've already done the valve cover gasket and oil filter housing gasket. My idle is stable and I don't have any starting issues. I also have noticed a whistling sound when accelerating. I now think the leaks are caused by my PCV not functioning correctly.

From what I gather, I'm supposed to have a slight vacuum when the engine is running, correct?

Well, I pulled off my oil cap when my car was running today. The engine's idle stumbled, but I noticed that there was air being forced out of the oil cap hole. Could this positive pressure be forcing oil out of the gaskets, such as the timing case seal?

Here is a video showing what's up. It's blowing air out of the oil cap hole.


I want to figure out a way to get rid of the PCV that will eventually fail. All I can see is there is a hose from the valve cover venting to the PCV. Then the PCV attached to the intake manifold and does what? Do the crankcase vapors feed into the intake manifold and get sucked right back into the engine? Can somebody help me figure out how the PCV is routed so I can make an oil catch can to get rid of the PCV?
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Old 01-15-2014, 08:22 PM   #2
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You can cut the hose connecting the valve cover and the PCV and put a large bolt and clamp in the end that connects to the PCV side to block it off. The car will run fine with the other end open to atmosphere although you will get a little condensation out of it while the motor is warming up. There will be positive pressure blowing out the hose on the valve cover side. If it is connected to the PCV that creates a slight negative pressure in the valve cover so that when you take off the oil fill cap it has slight suction but once the cap is off it will blow air out the hole.
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Old 01-15-2014, 10:01 PM   #3
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I don't want to vent to the atmosphere. From all I've read, BMW motors are designed to have a slight negative vacuum at all times. Somebody said something about low piston ring tension, and needing the vacuum, but I don't fully understand the concept behind that.

I also tested this on my X5 at school, since I left the 318 back home. It has a working PCV, which was replaced last summer, and it wasn't blowing air out of the oil cap when I removed it. People assured me that everything was working right in that case.

Now, I've been reading up on PCV and substituting in a catch can. When not venting to the atmosphere, the catch can system seems to create a lot of vacuum. Stock spec is 10-15 mbar, but this is enough to keep the cap stuck on the valve cover. I know too much is bad for an OEM M54 set up as it can suction oil from the pan and hydrolock, but a catch can eliminates that possibility. How much vacuum is too much for our engines, and when will it be bad?
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Old 01-15-2014, 10:43 PM   #4
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I can't answer that question for you. All I know is I redid all the seals in my m44 other than the head gasket and when I started it for the first time after all that work, the motor had some serious suction at the filler cap and I was blowing smoke big time. I ended up rigging the PCV the way I described to you and ran it for about 100 miles. The smoke went away and then I installed a new PCV and the motor is running great now. I think that the PCV or rather the CVV as BMW calls it is a bit different on our 4 cylinder motors than the 6 or 8 cylinders. I figure the concept is the same, but the valves are definitely different and I don't think that the 4 banger is known to have bad CVVs or that they can draw air in from the rear main seal like the M62s do when the valves go bad.
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Old 01-20-2014, 12:39 AM   #5
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Disconnect CCV valve hose and check for vacuum. If you have vacuum on the CCV I got bad news. When combustion blows out the oil cap when there should be a slight vacuum if the rings are sealing good. Excessive blow-by is because the piston rings are not sealing against the cylinder walls and combustion gases are filling the crankcase.

You can check this with a leak-down tester or do a compression test and then add a small amount of oil through the spark plug hole. If the compression jumps up with oil on the ring top side then you know the rings are letting the combustion gas past them. I prefer a leak down at 100psi and anything more then 5% is a high mileage engine. 10%+ leak down is a damaged cylinder. When you do the leak-down if a valve is leaking you will hear it, if it's a cylinder ring issue the blow-by will come out the oil cap
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