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Thread: positive crankcase ventilation

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    the BOSS of jellow supporter Feedback Score 0 a2j's Avatar
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    positive crankcase ventilation

    what should I do?
    broken ventilation system can cause oil cap leak?
    is there a way to check that pcv valve on the front valve cover?
    should I leave stock system? I don't want oil in pre-turbo pipe and rear turbo.
    what makes vacuum in the system? rear valve cover pass side nipple?

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    Stress free wheel gap. Not Verified Feedback Score 0 YoshiBishi's Avatar
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    I had a bad PCV valve which caused my oil cap leak. Replaced the PCV with a stock PCV and also got some Krank Vents and it seems to be fixed.

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    positive crankcase pressure is by no means always caused by broken piston / rings..

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    I AM IMPORT POWER Feedback Score 1 (100%)
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    Blowby, which occurs in all internal combustion engines and more so in Forced induction engines, causes crankcase pressure with is dealt with by the PCV system.

    -Chris

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    faulty pcv system can and will cause positive crankcase pressure, here is how it work. stock pcv valce is good for 16psi nothing more .


    The positive crankcase ventilation (PCV) system on our engines is designed to remove "blow-by" gases (unburnt fuel-air mixture that escapes past the piston rings on the compression stroke) from the crankcase before the gases can contaminate the engine oil or increase the crankcase pressure. Fresh, filtered air is supplied to the crankcase from the intake hose through the left (rear) rocker cover. This fresh air mixes with the blow-by gases and is sucked out of the right (front) rocker cover by the partial vacuum in the intake manifold through a metered orifice (or variable flow valve) called the PCV valve.

    As shown in the diagram , the PCV valve consists of a tapered plunger and two springs, and limits the air flow based on intake manifold vacuum. During idle and deceleration when blow-by gases are minimal, the low pressure (or "high" vacuum) in the intake manifold pulls the plunger against the springs and restricts the airflow through the valve. During cruising and low-load acceleration when blow-by gases are moderate, medium vacuum in the manifold only pulls the plunger part-way and allows more air through the valve. During acceleration and heavy-load operations when blow-by gases are at their maximum, low vacuum in the intake manifold allows the springs to keep the plunger "back" for maximum airflow through the PCV valve. In the case when the intake manifold becomes pressurized, such as during boost on turbocharged engines or during backfire, the plunger's seat is forced against the valve case preventing air from entering the crankcase. During extremely-high engine load the volume of blow-by gases may exceed the ability of the PCV valve to draw the vapors out of the crankcase. In addition, when the manifold is pressurized blow-by gases cannot leave through the PCV valve. In both of these situations the blow-by gases flow out of the rear rocker cover into the intake hose.

    http://www.stealth316.com/2-krankvents.htm
    Last edited by mb7050; 02-25-2011 at 10:15 AM.

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    the BOSS of jellow supporter Feedback Score 0 a2j's Avatar
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    Quote Originally Posted by Import Power View Post
    Blowby, which occurs in all internal combustion engines and more so in Forced induction engines, causes crankcase pressure with is dealt with by the PCV system.

    -Chris
    yes, I know why I need this. I had specific questions and I'd like to get an answers some how. or a diagram how it works, or something. I wanna put a catch can possibly. I heard something about leaving all 4 nipples open to the atmosphere.

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    its all up to you, what you prefer ..

    http://www.3sgto.org/f13/crankcase-v...tion-1042.html
    Last edited by mb7050; 02-25-2011 at 10:44 AM.

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    Hmmm you guys have some strange ideas about PCV.

    YES PCV can be overwhelmed by bad rings/piston, and usually IS on higher mileage engines.

    After the combustion side there is another "pump" in the engine. As pistons go up and down there would be pressure in an unvented engine. Before PCV there was just a tube for crankcase air to go so before pollution control, nobody cared. Now when the pressure rises in the crankcase it gets exhausted out the ONE WAY PCV valve. Those vapors exit into the intake. With an engine in good condition, the system works well with no problems. When you get excessive blowby which gets even worse under boost, the system is overwhelmed so hoses pop off, oil spews out the filler cap and the intake gets "lubricated."

    I've also heard about quality and fitment issues on some of the aftermarket PCV valves so compare carefully when changing an OEM for aftermarket, to prevent further problems.

    -SP

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    Forum User Not Verified Feedback Score 0 cjbyron's Avatar
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    Just take the PCV off and check it. Is the checkball loose (rattle ok)?
    Does it allow pressure out but keeps vacuum in? Blow away from engine but block it coming inwards.

    The problem with some aftermarket replacement PCV valves is they are backwards. Just be aware.

    So before worrying about things like bad pistons/rings from a leaky oil cap (LOL) just check your PCV which is extremely easy.
    Stock system works fine unless you want to upgrade. Before worrying about "oil in the intake/preturbo" look and see if you're even blowing any oil in there. IOW - check it out before worrying about it or plans to change it.

  10. #10
    Padawan garage troll Not Verified Feedback Score 1 (100%) Roybatty's Avatar
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    I was having pressure in crankcase (causing oil leaks @ valve covers, etc) and smoking on decel. My issues were resolved after ensuring PCV was working (rattles), my catch can flowed freely and had a minimum fitting diameter of 3/8", routed between rear valve cover and intake bubble.

    Still considering increasing port sizes on rear valve cover and intake bubble to match 19mm catch can fittings.

    Good readings on this thread and the links.
    Last edited by Roybatty; 02-25-2011 at 01:03 PM.

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