PCV Causing Vacuum Leak
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Senior User
Joined: Aug 2004
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From: Nassau Co. NY
PCV Causing Vacuum Leak
So I was was tired of trying to tune my Holley 650 and finally threw in the towel and got a 600 Edelbrock. When the holley was on there the engine had the slightest surge but I was never able to pin down a vacuum leak. The PCV valve made quite the racket while running.
Now the edelbrock is on there and no matter what I did I could not get the idle below 750 (4 speed truck). I checked the carb, manifold, hoses, and boosters and no vacuum leaks. I disconnected the PCV port at the carb and plugged it and it immediately stalled.
I went down to the local speed shop and got a new PCV grommet that has a small opening (restricting) and some foam filter material in it. Got home and popped it in and the idle dropped right down to a near stall. Adjusted the screw and she's running fine.
Now for the question. Did I fix the problem or just band aid it? Has anyone heard of having to restrict the PCV circuit?
Now the edelbrock is on there and no matter what I did I could not get the idle below 750 (4 speed truck). I checked the carb, manifold, hoses, and boosters and no vacuum leaks. I disconnected the PCV port at the carb and plugged it and it immediately stalled.
I went down to the local speed shop and got a new PCV grommet that has a small opening (restricting) and some foam filter material in it. Got home and popped it in and the idle dropped right down to a near stall. Adjusted the screw and she's running fine.
Now for the question. Did I fix the problem or just band aid it? Has anyone heard of having to restrict the PCV circuit?
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From: VA
From your description I'm not sure I know exactly what went on, but it sounds as if your PCV was sucking too much crankcase gasses/air. A PCV is just a controlled vacuum leak, sounds like you cleared up the issue by fixing the amount of air that te PCV is drawing. Sounds like a valid fix to me.
Lead Driver
Joined: Nov 2000
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From: Albuquerque
I've been known to restrict the PCV valve air supply in order to improve idle quality. The valve is basically a metered air leak that doesn't pass through the carb.
Newer engines tend to be setup that way. This also helps with minor oil leaks etc. due to crankcase vacuum.
Newer engines tend to be setup that way. This also helps with minor oil leaks etc. due to crankcase vacuum.
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Joined: Dec 2001
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From: Louisville,Ky.
Gotcha. I have had several over the years that opened up different amounts. Some open maybe 1/16" and others up to 1/4".
If you got it running good, that's all that really matters.
If you got it running good, that's all that really matters.
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Joined: Aug 2004
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From: Nassau Co. NY
Well I guess it wasn't pulling enough cause I "found" a bunch of new oil leaks. 
Gonna pull the foam out of the baffle and see how she reacts to that.
Gonna pull the foam out of the baffle and see how she reacts to that.
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From: VA
Does this mean you'll also be replacing a few gaskets (valve cover/oil pan gaskets)?
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From: Louisville,Ky.
Some compression is leaking past the rings. My old 460 I had would blow oil out of the dipstick at prolonged highway speeds unless I used a pcv valve that opened a lot and sucked the blow-by into the intake instead of out of the dipstick or valve cover breather.
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From: VA
Run it and put your hand over the PCV hole in the valve cover. If you feel any pressure, there's probably too much blowby, if not then it's probably fine. Also, no need to even put your hand on it if you can literally see the blowby coming out.
The PCV valve was probably just too blocked up with what you'd done to it. I doubt you have excessive blowby if the engine's so new. Did you rebuild it or buy a short/long block?
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From: Nassau Co. NY
Ok so I had it running and pulled the PCV/oil cap. Whats excessive? I see a little vapor coming out but I can't feel any pressure with my hand. Its not puffing like a steam engine or anything. I pulled the foam out of the baffle and the idle came up a little but is still ok.
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From: VA
Ok so I had it running and pulled the PCV/oil cap. Whats excessive? I see a little vapor coming out but I can't feel any pressure with my hand. Its not puffing like a steam engine or anything. I pulled the foam out of the baffle and the idle came up a little but is still ok.
Where did you buy the long block? Just wondering for my own interests. Trying to find myself an engine.