How to check PCV lines for vacuum (cheap way)?

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430
Location
Switzerland
Hi, I'd like to check my PCV hoses for vacuum to see how much suction is created by the intake manifold. I thought about simply running the engine at idle and disconnecting the pcv hose from the intake duct and putting my finger to sense vacuum force. I guess this would work but by disconnecting the PCV hose I open the circuit and hence blowby gases are no more sucked out of the crankcase. Of course I don't plan to do that for a long time but do you think it may hurt anything? Any other way to check how much vacuum is in the PCV hose (without a gauge)?
 
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1,574
Location
Alamo, CA
If its old I just buy new fuel hose and replace it for $2. If its not old , you can jus take off both ends for inspection and blowthrough.
 

JTK

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13,363
Location
Buffalo, NY
If you pull the PCV hose off the barb on the intake manifold you will have such a massive vac leak that your vehicle probably wont run or will instantly stall. You could pull the PCV valve out of the cam cover to feel for a vacuum on the business end of the PCV valve if you wish. You can run the engine at idle that way (temporarily) without issue. Joel
 

kilou

Thread starter
Messages
430
Location
Switzerland
Thanks for your replies. However putting the finger on the pcv hose may only show how much vacuum is created by the intake manifold. On the other hand I may remove the oil dipstick and plug the hole with my hand feeling for vacuum there. This would check if vacuum can reach all the parts of the PCV system right?
 
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6,162
Location
Illinois
Your PCV valve should limit the vacuum . I run a closed crankcase and it will develop about 10" Hg when the intake manifold is under it's highest vacuum, ~20"Hg. Just put a tee in the line and connect a vacuum gage.
 

kilou

Thread starter
Messages
430
Location
Switzerland
Quote:
Your PCV valve should limit the vacuum . I run a closed crankcase and it will develop about 10" Hg when the intake manifold is under it's highest vacuum, ~20"Hg. Just put a tee in the line and connect a vacuum gage.
I'm not sure my car has a PCV valve. I have renewed all the components of the PCV system this weekend and there is no valve anywhere, only an oil trap and hoses. Do PCV valve only appear on turbo cars??
 
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19,479
Location
Chicago Area
The gauge for a PCV system is hooked up on the INLET, which is generally on the valve cover. You want neg pressure there when at cruising or idling conditions.
 

kilou

Thread starter
Messages
430
Location
Switzerland
It seems that vacuum is best checked at the oil dipstick since it will accurately measure vacumm in the crankcase. Can you recommend a suitable cheap vacuum gauge (I don't know how much negative pressure I should read in the PCV) that Imay use to check that??
 
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