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Crankcase ventilation system

What is it? I mean is it a devise, a valve or something? I was told that if it fails that it could send crankcase pressure into the intake?!?! Is this true?
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Old 03-21-2003, 10:41 AM
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Crankcase should be at slight vacuum because intake draws off the oil vapors or whatever gas is in there. It's supposed to go to intake. Intake is what ventilates it.
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Last edited by Lawrence Coppari; 03-21-2003 at 11:17 AM..
Old 03-21-2003, 11:12 AM
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While we are on this...how much 'draw' is normal ? I have been chasing a hesitation issue for sometime and pressurized the intake and got a lot of flow through the Crankcase vent system. When I plugged the vent line at the J boot, I couldnt finde any vacuum leaks.
When at Idle, If I remove the filler cap the Idle picks up and is rougher. Is this normal?
I was thinking the hesitation might be from drawing too much from the crankcase vent line, perhaps something is wrong allowing too much to be drawn. I have thought of inserting a PVC valve in the vent line to limit the amount it draws.
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Old 03-21-2003, 04:06 PM
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Dude, wheres the vent line?
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Old 03-21-2003, 05:45 PM
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It's the biggest vacuum line on the car, I think it was ment to handle the extra blowby on start/warm up so that you don't pop your dipstick out or blow you seals. Your Idle picks up and is rougher because you are drawing in "false air" that your injection system isn't designed to compensate for. That's why your block is air tight
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Old 03-21-2003, 10:34 PM
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When I pressure tested the intake with 10psi, there was a lot of air 'flowing' thru the vent line, no leaks at the hoses or oil separator. If the block is air tight...then where could it be flowing?? Is there somewhere on the block that could be leaking air and causing a vacuum leak thru the crankcase vent system?
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Old 03-22-2003, 02:41 AM
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Quote:
When I pressure tested the intake with 10psi, there was a lot of air 'flowing' thru the vent line, no leaks at the hoses or oil separator. If the block is air tight...then where could it be flowing?? Is there somewhere on the block that could be leaking air and causing a vacuum leak thru the crankcase vent system?
This is not really a problem. The reason you get air leaking is because you are pressurizing many areas that aren't meant to see that kind of pressure, but instead a slight vacuum. One of these is the air/oil seperator. The air/oil seperator is designed to seal under a vacuum. When you apply pressure to it, you are actually pushing the snapped-on cap away from the o-ring. In contrast, when under a vacuum, the lid is actually sucked down onto the o-ring.

Personally, I don't like pressurizing the crankase. Look at the size of your oil pan and estimate the force you are appliying by pressurizing the crankase to 10 psi. I wouldn't think this would be very good on the oil seals and gaskets as well, since you are essentially trying to blow them out. Thus, I now allways disconnect the line going to the seperator before checking the intake system for leaks.

Rob
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Old 03-22-2003, 05:46 AM
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also it could be going out around the piston to the exhaust valves if they're open
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Old 03-22-2003, 07:17 AM
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There is an elbow on top of your filler vessel. My old one had cracked so I replaced it some time ago.
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Old 03-22-2003, 07:29 AM
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