Pancake valve flow direction

[erykv1]

Hey guys,

Quick question.

If you disconnect the PCV / pancake valve while the car is running at idle, is it normal for there to be a strong vacuum on the end of the valve.



Vac is constantly pulled from the red arrow, so vaccum on the PCV valve should be normal right?

Read through the self study guide and it doesn't seem to be too clear.

I've been hearing a short hiss when turning the car off and I'm wondering if my PCV valve could be bad. However I'm not noticing any common bad PCV valve symptoms (rough idle, oil leaks etc)

Thanks!

[cjt671]

At idle blow by is not directed to the pressure regulating valve (pancake). It is sent directly to the intake manifold and during boost the pcv valve closes and directs flow through the pancake to the y pipe.

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[erykv1]

so if I am getting suction at the pancake, the valve is bad?

[airjawed]

Where are you disconnecting it? between valve and y pipe or at 51 in diagram?

The pancake valve actually allows air both ways depending on if boost is present or not. I believe it allows very little air one way but a lot the other... have to read up on it again.

[erykv1]

Where are you disconnecting it? between valve and y pipe or at 51 in diagram?

The pancake valve actually allows air both ways depending on if boost is present or not. I believe it allows very little air one way but a lot the other... have to read up on it again.

Disconnecting it from the Y-pipe where the blue circle is.

-edit- doesnt seem like I can buy this valve by itself, but at this point I'm willing to buy a complete assembly. been chasing this issue for far too long.

[cjt671]

What issue are you having? The purpose of the valve is to limit vacuum in the crankcase so it isn't a one-way valve. It is meant to limit vacuum going in the direction away from the y pipe

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[erykv1]

What issue are you having? The purpose of the valve is to limit vacuum in the crankcase so it isn't a one-way valve. It is meant to limit vacuum going in the direction away from the y pipe

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So if I disconnect the Y pipe and put my thumb on the pancake valve and there is a ton of suction, then the diaphram inside is most likely torn right?
Been chasing some crazy MAF readings / fuel trim issues. Zero Boost leaks on the car so I'm thinking its internal.

[cjt671]

So if I disconnect the Y pipe and put my thumb on the pancake valve and there is a ton of suction, then the diaphram inside is most likely torn right?
Been chasing some crazy MAF readings / fuel trim issues. Zero Boost leaks on the car so I'm thinking its internal.

I don't think it should be a large amount suction honestly.. mine definitely doesn't.

But maf reading issues and fuel trim issues make me think bad maf or egts. I recently battled this problem. Are you having misfires at part throttle?

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[MacDaddy]

If you think its bad a brw one is like $7 on ali-express

[erykv1]

I don't think it should be a large amount suction honestly.. mine definitely doesn't.

But maf reading issues and fuel trim issues make me think bad maf or egts. I recently battled this problem. Are you having misfires at part throttle?

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zero misfires, car just feels like it has no balls. if you search through my recent threads you can find some in depth info as to whats going on.
in summary, my car has zero boost leaks (unless internal). egt's are coded out, and i've tried 3-4 MAF's and they all do the same thing.

was hoping it was the pancake valve... but i'm unsure at this point.

[S4tech2]

I don't think it should be a large amount suction honestly.. mine definitely doesn't.

But maf reading issues and fuel trim issues make me think bad maf or egts. I recently battled this problem. Are you having misfires at part throttle?

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I'm having similar issues after being on the interstate a little while. It's like really bad misfires at 30% throttle but will clear up if I push to wot, I have faults for egts and map sensor.

[cjt671]

I'm having similar issues after being on the interstate a little while. It's like really bad misfires at 30% throttle but will clear up if I push to wot, I have faults for egts and map sensor.

Same exact issue I just had. New maf solved my problem. But I also replaced map, n75, and am going to change my egts.

Bad egts could cause misfire as they would cause the car to run rich. You should replace map and egts/fix the issues causing the codes. If that doesn't help I would look into maf issues but make sure it's not plugs coil packs or a boost/vac leak. Quick test you can do is disconnect the maf and see if the misfires are still there. If not I would believe your maf or a boost leak is the culprit.

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[cjt671]

I'm having similar issues after being on the interstate a little while. It's like really bad misfires at 30% throttle but will clear up if I push to wot, I have faults for egts and map sensor.

http://www.audizine.com/forum/showthread.php?t=698426


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[S4tech2]

I had n issue with one of the O2 sensors wiring, fixed that but had this issue, only does it every so often which makes if difficult to pin point. I believe my air filter is oiled which may be the culprit. ITG filter. Sorry I feel like I kinda jacked the thread.

[erykv1]

can someone verify this diagram i threw together? is this the correct flow for IDLE conditions?

the intake manifold line check valve should allow flow into the intake manifold but not out.

with all that being said, is it not correct that the pancake valve should have some vacuum on it?

[zillarob]

Your drawing is correct for off boost operation of the spider, except the mani port is the vac source and the one you have labeled as valley pan is to vent the block.

There will pretty much be full mani vac at it if plugged.

[erykv1]

Your drawing is correct for off boost operation of the spider. There will pretty much be full mani vac at it if plugged.

so if i pull off the pancake valve from the Y-pipe, there should be vacuum on it correct?

[zillarob]

Yup.

[airjawed]

Yup.

so if i pull off the pancake valve from the Y-pipe, there should be vacuum on it correct?

Well... it should be vacuum at idle but it should be a low amount of flow... it should not act like a straight tube to the intake manifold. I took mine off just now to see and it did flow but in a controlled way.

In a state of boost the check valve in the intake manifold tubing will stop positive pressure from entering the hoses. In this state the pancake valve will then act in reverse and draw air into the y pipe(not a large vacuum force but a vacuum nonetheless in that direction).

This dual vacuum source is similar to most vacuum lines in our boosted cars. Vacuum is not always present in the intake manifold and thus an alternate vacuum source is needed during boost. My brakes (automatic trans) get vacuum from an electric pump for example. Another example is the EVAP system getting vacuum from the turbo inlet side.

Pancake valve is hard to test so the manual doesn't go in depth about it.

If you think yours is a problem then I would just block it off(temporarily shouldn't be an issue).

[zillarob]

Ixnay on the block it off, bad juju

[erykv1]

Well... it should be vacuum at idle but it should be a low amount of flow... it should not act like a straight tube to the intake manifold. I took mine off just now to see and it did flow but in a controlled way.

In a state of boost the check valve in the intake manifold tubing will stop positive pressure from entering the hoses. In this state the pancake valve will then act in reverse and draw air into the y pipe(not a large vacuum force but a vacuum nonetheless in that direction).

This dual vacuum source is similar to most vacuum lines in our boosted cars. Vacuum is not always present in the intake manifold and thus an alternate vacuum source is needed during boost. My brakes (automatic trans) get vacuum from an electric pump for example. Another example is the EVAP system getting vacuum from the turbo inlet side.

Pancake valve is hard to test so the manual doesn't go in depth about it.

If you think yours is a problem then I would just block it off(temporarily shouldn't be an issue).

Mines making enough vacuum enough to cold a credit card in place.

I also noticed my dipstick smells like fuel. Could be a byproduct of running rich... but could be the rebuilt spider hose as well.