PCV Valve revisited - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


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Old 02-07-2005, 11:01 AM   #1
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Default PCV Valve revisited

Well, I took advantage of the weather this last weekend, and pulled and cleaned a few parts, hoping to get the Check Engine Light to go away.

One of those parts was the PCV Valve. Now, on to the question...

You shouldn't get straight airflow through the valve, should you> I mean the whole point of the thing is to regulate pressure. But the one in my car allows straight airflow either direction (yes, fo what ever reason, I blew through it).

It'* a cheap enough part that I'll probably get a new one on the way home no matter what, but I figured I'd ask all the same.

BTW, I did Google this, but no site I could find mentioned airflow...
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Old 02-07-2005, 03:43 PM   #2
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Should be a spring loaded one-way valve, I think. When you blow on the little end, should be closed, but blow on the big end, it should open up. Shake it, it should rattle.

BTW, thanks for your earlier PCV question. I learned that my '95 should have a spring and 2 o-rings. All I had was the big seal. This car has not been treated well. Wait'll I post a pic of the throttle body
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Old 02-07-2005, 04:16 PM   #3
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I changed mine a few days ago.
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Old 02-07-2005, 04:18 PM   #4
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Thanks for the reply, but I think you may have it backwards (at least by my thinking, which is always supsect)

Since the big end actually points towards the engine, I would think that would be where the resistance is. The one I got rattles like it'* supposed to, but I just have a gut feeling I shouldn't be able to just blow air through it....

And I'm glad my last post helped. I hate sounding/feeling clueless about such a simple part, but I never paid attention to how these things work. I just put a new one in each year (or so).
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Old 02-07-2005, 04:33 PM   #5
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Mine isn't spring loaded. Just rattles in there.. air comes OUT the plastic elbow, and goes IN the bottom [large] hole where it sits in the Intake.


-justin
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Old 02-07-2005, 07:58 PM   #6
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Thanks, Don. I thought my Chilton'* pictured the PCV for my car, but on closer inspection, I find every one BUT my '95. (Gotta get an FSM for this thing) So, I'm supposed to have an o-ring under the shoulder of the valve, and a big o-ring to seal the cover and that'* it?

Hey MOS, you makin' me crazy...Had to go out to the garage, take out the valve and blow on it again. I don't know what yours does, but mine works as I said. It makes sense that way, too. The crankcase fumes go in the big end and are sucked through to the intake through the small end. It may not have a spring inside, it may just be weighted to calibrate for this engine, but it acts like a spring in that the weight tends to keep the valve closed.

Umm...kids, don't try this without wiping off the pcv valve body first- ptooey!
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Old 02-07-2005, 08:07 PM   #7
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OK, here is a better way to say it. The valve allows a calibrated flow from the crankcase to the intake manifold, and prevents flow in the opposite direction.
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Old 02-08-2005, 02:01 AM   #8
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I hope you guys are testing new PCV valves, old motor oil taste horrible. LOL

Bill is correct on how the air flows in the fat end out the small end to the intake. When you crank the car manifold vacuum pulls the PCV valve plunger up, against spring pressure, to the closed position. In the closed position a metered amount of air is allowed to leak by. As the throttle opens and manifold vacuum drops the spring pushes down on the plunger and allowing more air to flow.
Take a pencil and push the plunger to the small end of the valve then see how much air you can blow through it. That will be the amount of air leakage the motor will see at idle.
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Old 02-08-2005, 09:11 AM   #9
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That last post actually helped a lot! I may have had the airflow theory backwords, but I don't need a pencile to push the plunger. It just flaps around. Sounds like the internal spring is shot.

Gues I gotta spend the 5 bucks for a new one....

Thanks everyone for all the input. And especially Bill, for making me NOT the only one who'* blown air through thier PCV Valve. I'm not the only freak in the crowd this time!!
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Old 02-08-2005, 11:28 AM   #10
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Default PCV

Get the Delco is you want OEM performance.
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