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Discussion Starter · #1 ·
EFI, have both the PCV and distribution manifold hosed to connections under the upper intake. Only take-off from distribution manifold is to fuel regulator. When I hook up the vac gauge to distribution manifold and start the engine, vac jumps to 20" then slowly recedes to the 9-11 range and hovers there. I've checked all hoses and have sprayed starter fluid (ether) all around with no effect on revs. Anything else to look for, diagnose?
 

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Dale, If you are trying to read vacuum at the same place as the PCV it is going to be low. At idle the PCV is a vacuum leak of sorts. The engine vacuum pulls the PCV open so it can evacuate crancase emissions (normal operation). So I think you would need to isolate the vacuum distribution block from the PCV. You could plumb the vacuum distribution block off of another vacuum port on the intake manifold.
The PCV is typically routed with no taps in the vacuum line Just a straight shot from intake manifold to PCV finally the valve cover.
Pull the PCV valve out and stick your finger over the end to stop the vacuum leak and check your vacuum reading now. Is it higher and more stable?

Michael S.
 

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Dale, I found this image and it shows the PCV totally isolated from all other vacuum routing.

 

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That's a classic symptom of a vacuum leak, so it sounds like you're on the right track. Does it run rough? Might be the intake gasket.
 

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Discussion Starter · #5 ·
The PCV and FPR are each hooked to a sepatate vacuum source. I'll try pinching off the PCV next time.

Thanks for the diagram.

Will be pulling engine this winter & in addition to other issues will pull intake & change gasket. But if the intake gasket was leaking (or any vacuum leak, for that matter) wouldn't the starting fluid pick it up?
 

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Discussion Starter · #7 ·
So, I need both valve covers vented? Currently only one is vented (to atmosphere, but I'm going to vent it to the air intake before the TB). The other has a rubber grommet-type plug.
 

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Dale one valve cover will have the pvc valve in it. Other cover will have a breather in it. Only one needs to be vented.You don't want to vent the same cover the pvc valve is in.Breather can go to atmosphere or to air cleaner like on some carbed versions.
Can you check vacum at a different location? Seems hard to believe you actually have a vacum leak as engine would definetly run rough if going from 20-9" of vacum. Also if having a bad leak it would probally never reach 20 when starting but be low from the get go. May be a clogged port or collapsed hose but does'nt seem as you are reading actual manifold vacum as tested.
What does gauge read when motor held at 2-2500 rpm?
 

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Discussion Starter · #9 ·
Will check later for vacuum @ 2500.
My PCV valve is installed in the rear of the block behind the intake and is connected by dedicated hose from PCV to upper intake. As mentioned, only my pass. side valve cover is vented; this is the one I was going to connect between air filter anf throttle body.
 
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