dominic
1/2 ton status
I got a 77 chevy pick-up with 400 sb and the pcv valve keeps tapping real fast at idle speed.Making a metalic noise...any ideas what could cause this?
CK5
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PCV Valve going crazy
- Thread starter dominic
- Start date
Lots of blow by from the rings would be my guess, might be time for a compression test.
Sounds like the valve is bad. Quick and easy to swap and cheap also.
I've had a few do that....it might be the valve itself has a busted spring inside it...or the vacuum hose might be restricted or collapsing inside...one engine I had that turned out to have a dead cam lobe on the #1 exhaust valve made the PCV valve start "chattering",and it stopped after I replaced the camshaft..a leaky intake valve might caise "blowback" into the intake and the PCV valve is intended to close up if a backfire or feedback occours and the spring in it makes it "click" and shut to prevent blowby gasses from being ignited...A compression test will show any cylinders that aren't up to snuff,but a dead cam lobe wont show up under a compression test most of the time..looking at how ear the rocker arms go up and down is the easiest way to check them with the valve covers off...sometimes a rocker arm stud pulls out of the head and gives the same symptoms as a bad cam lobe...if you see one with many more threads showing past the nut,thats a sign it has pulled up out of the head...
dominic
1/2 ton status
I change the pcv valve before and it still did the same thing,I will do compression check in a few days to see,I will let you guys know what comes up. thanks for the info.
In the meantime, pull the vacuum line off and put your finger over it lightly. I'm betting you will feel pulsing vacuum.
Or lay your hand lightly over the throttle body intake. Don't close it off, just feel the air flow. You should feel a nice even suction.
Odds are you will feel a bobble. Sounds like you have an intake valve sticking or burned, or not closing right for some reason.
Or lay your hand lightly over the throttle body intake. Don't close it off, just feel the air flow. You should feel a nice even suction.
Odds are you will feel a bobble. Sounds like you have an intake valve sticking or burned, or not closing right for some reason.
My 454 has the same rattling PCV valve. A new valve made no difference, all the rocker arms mave the same, its been noisy for the 3 years I have had it. 
