PCV Valve pulsating

[Cricket]

Is it normal for a TBI PCV valve to pulsate or "rattle" at idle?

Mine is rattling/pulsating and I'm wondering if this might have something to do with the crankcase over pressurizing. Possibly a blockage in the throttle body?

 

[rcamacho]

Normal in my experience. Depends upon vaccum leve the valve is tunef for.

 

[Jason4x4]

it's just working properly

 

[dyeager535]

They can rattle, (test is to shake them and see if they do) but unless I'm mistaken, at a steady state (like idle) the valve should not rattle at all, but hold in a steady position, since vacuum is how it operates. If vacuum is steady, so too should the valve I would think.

 

[Cricket]

I pulled it yesterday, turns out the rattle is a valve cover/PCV vibration. If I hold it in my hand the valve remains steady.

 

[dyeager535]

Are your valve covers and related plumbing (PCV hose, breather) all stock? Is the PCV grommet good enough that there is little potential of air getting in there?

 

[Cricket]

Yep, the grommet is tight. I might try adding a longer hose to the throttle body, the stock hose is a hair short and I think it's causing the PCV to sit at a slight angle.

Not enough for air to leak past IMO.

 

[dyeager535]

Where I'm going with that is that I know the MAF (TPI) setups will have a screwed up idle if you the crankcase is vented other than stock.

Since PCV is essentially a vacuum leak (although expected) I would think even on a MAP setup opening say the filler cap (or leaking breather/PCV grommet) might affect MAP readings, and thus idle quality. I'm curious if any TBI folks have tested this. I thought maybe someone did, but can't find it via search...

 

[Cricket]

Well I know when I pull my oil cap or PCV at idle there's no discernible change. I would think that the MAP would be reading intake pressures and unless you had some really bad rings wouldn't be an issue.

I should use that smiley more often when it comes to TBI although I'm getting more knowledgeable every day.

 

[dyeager535]

Should be along the same lines as EGR as I see it, since MAP is used to see if the EGR valve (vacuum leak) is open when it's commanded. Since the PCV pulls from a "closed" source (inlet/outlet for circulation is standardized) venting the crankcase improperly I would *think* would be a vacuum leak.

With the PCV out, don't you get suction on your finger if you put it over the bottom of the valve?? PCV is pulled from under the throttle blades, so should be manifold vacuum, right?

 

[Cricket]

Should be along the same lines as EGR as I see it, since MAP is used to see if the EGR valve (vacuum leak) is open when it's commanded. Since the PCV pulls from a "closed" source (inlet/outlet for circulation is standardized) venting the crankcase improperly I would *think* would be a vacuum leak.

With the PCV out, don't you get suction on your finger if you put it over the bottom of the valve?? PCV is pulled from under the throttle blades, so should be manifold vacuum, right?

Yes, there is vacuum at the PCV. I'm trying to remember the guts of a block, the EGR sits on the manifold and those ports lead into the head right? As in "exhaust gas recirculation". So there is no open port into the crankcase per se.

Almost forgot:

 

[dyeager535]

I believe Chev pulls EGR from the exhaust crossover in the TBI apps, which is then dumped into the intake, but not sure where/how. Might just be a big hole (or two in dual planes) that feeds each half of the manifold.

In my TPI setup, it's pulled from an exhaust tube, and small holes are drilled in each runner that feed that to the cylinders. Same idea, different execution.