No Vacuum @ PCV Valve

No Vacuum @ PCV Valve

Postby castle_Rock [OP] » July 5th 2010, 2:16am

Alright, I checked the PCV valve & found no vacuum when the engine was idling at normal temp when I placed my hand over the valve. What hoses in particular should I check for to see if their plugged up. Anything else needs to be checked as well?

I also shook the PCV valve as well, & heard it rattle, which is a good thing.
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Re: No Vacuum @ PCV Valve

Postby Mr_Bowtie » July 5th 2010, 4:42am

PCV isn't open that much at idle. Its open more when its under load. Did you take that line off the PCV and check for vacuum?

Good read on the PCV valve:
http://www.aa1car.com/library/pcv.htm
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Re: No Vacuum @ PCV Valve

Postby 979roadrunner » July 5th 2010, 4:49am

Don't know how common it is on an Astro, But pre 94 Caprices with 5.7L V8s (police interceptors) would sometimes get carbon build up in the PCV passage in the throttle body. Just a thought.
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Re: No Vacuum @ PCV Valve

Postby castle_Rock [OP] » July 5th 2010, 5:27pm

Mr_Bowtie wrote:PCV isn't open that much at idle. Its open more when its under load. Did you take that line off the PCV and check for vacuum?

Good read on the PCV valve:
http://www.aa1car.com/library/pcv.htm


Thanks for the Link Bowtie - I removed the Valve by the boot as a whole to check for suction, but didn't take the valve itself off to check.
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Re: No Vacuum @ PCV Valve

Postby Astroplane » July 6th 2010, 7:26am

castle_Rock wrote:What hoses in particular should I check for to see if their plugged up. Anything else needs to be checked as well?

At idle, there should be enough flow at idle to suck your thumb a little on the intake side of the PCV valve. W or Z engine?
The price of paying attention is cheap considering the alternative.
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Re: No Vacuum @ PCV Valve

Postby castle_Rock [OP] » July 7th 2010, 5:30am

Its a Z engine.
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Re: No Vacuum @ PCV Valve

Postby astroturf » July 7th 2010, 6:11am

castle_Rock wrote:Its a Z engine.


Is there vacuum at that port at idle?
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Re: No Vacuum @ PCV Valve

Postby Astroplane » July 7th 2010, 8:32am

If you remove the PCV hose at the TBI, the idle RPM should increase almost to mid-range. If not, and now that we know this is a Z, the port is restricted with carbon buildup.
The price of paying attention is cheap considering the alternative.
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Re: No Vacuum @ PCV Valve

Postby castle_Rock [OP] » July 7th 2010, 5:38pm

Astroplane wrote:If you remove the PCV hose at the TBI, the idle RPM should increase almost to mid-range. If not, and now that we know this is a Z, the port is restricted with carbon buildup.


I remember removing the PCV hose from the valve, & it came off the TBI by accident when I first checked it - I don't think the RPM went up once it was disconnected. So it be carbon buildup. Should the hose be disconnected from the TBI while leaving the pcv connected to the valve? Or does it matter?

Thanks

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Re: No Vacuum @ PCV Valve

Postby Astroplane » July 8th 2010, 9:22am

It doesn't matter. You have no suction at the PCV valve and there was no vacuum leak when it came off the TBI. Time to remove the TBI unit and clean the vacuum passageways. You will need a TBI base gasket, carb and choke aerosol cleaner, drill bits that match the ports' inner diameter, compressed air if possible, and a new hose for the PCV (if needed). Reinforced fuel hose sold by the foot at the LAPS will not hold up for long to the heat and oil vapor present in the PCV circuit. It will work, but the hose will become hard and brittle.
The price of paying attention is cheap considering the alternative.
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Re: No Vacuum @ PCV Valve

Postby castle_Rock [OP] » July 8th 2010, 4:39pm

alright, thanks AstroPlane -
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