Whipple PCV/venting

[whipplenight]

Hello, long story short I was getting a cylinder 8 misfire I went to swap coils and plugs and I found the problem staring at me. The whipple had a puddle of oil sitting behind the throttle body! The catch was filling up very quickly and putting oil back into the intake. So I decided to run a metco oil cap breather with check valve and after installing it I noticed something strange, the one way valve was being held down as if it was under vacuum...I put my hand over where the oil cap would be and it was definitely sucking air...I’m running a catch can one hose to PCV and one hose to whipple barb behind throttle body. I’ve blocked off the factory barb under the oil cap whipple designed this to run from the barb to the air box. I have a carbon fiber intake so this wasn’t possible so I just ran a hose and filter on it, but after getting the metco breather I capped off this fitting. Any ideas on why I’m under vacuum? To my knowledge I should be releasing crank case pressure not sucking air...

 

[ScLeCo]

It just depends on how much boost is being generated/rpm/throttle position. Get a boost gauge and watch it most of the time under partial throttle you're actually in vacuum.

Here this explains it better.
https://www.autometer.com/blog/what-benefit-is-a-vacuum-boost-gauge-over-a-boost-only-gauge/

 

[whipplenight]

This is happening at idle in park. It just doesn’t make sense if the system is intended to be under vacuum then why did whipple run the vent hose to the air box? Also if the system is always sucking the check valve tight causing a seal how is it supposed to relive crank case pressure?

 

[Wild one]

This is happening at idle in park. It just doesn’t make sense if the system is intended to be under vacuum then why did whipple run the vent hose to the air box? Also if the system is always sucking the check valve tight causing a seal how is it supposed to relive crank case pressure?

It sounds like you might need to open up the fitting again that you capped.The system needs a make up air inlet that should allow filtered air back into the crankcase to compensate for the air that is sucked out of the crankcase .I'm just guessing but if it was me,i'd put the filter back that you had on it earlier and see what happens.Hopefully Tach Tech sees this,as he's got a fair bit of knowledge about the principles behind making the PCV system functional with a whipple

 

[ScLeCo]

This is happening at idle in park. It just doesn’t make sense if the system is intended to be under vacuum then why did whipple run the vent hose to the air box? Also if the system is always sucking the check valve tight causing a seal how is it supposed to relive crank case pressure?

The crank case needs to breathe. Think of it as you breathe. You inhale and exhale, your crank case needs to do both too. Take the check valve out of the valve cover breather.
That valve cover breather needs to be able to draw in filtered air.

 

[Tach_tech]

At idle the breather portion will be under slight vacuum, that’s normal operation of the PCV/breather system. It’s not until your under moderate to heavy load that the PCV valve opens allowing flow.

When are you getting the #8 misfire? Is it enough to actually set a CEL or are you monitoring for misfires.

Both me and my buddies truck will show some misfires, mainly cylinder 8 at WOT and near redline. I’m not convinced it actually misfires as it runs perfectly under load. I went through swapping everything as well with no change. So I’m not convinced there’s an issue, unless it’s related to an airflow flaw in whipple a design. I have heard from people that when you get into boosted engines that misfire monitors can be slightly inaccurate.

 

[whipplenight]

At idle the breather portion will be under slight vacuum, that’s normal operation of the PCV/breather system. It’s not until your under moderate to heavy load that the PCV valve opens allowing flow.

When are you getting the #8 misfire? Is it enough to actually set a CEL or are you monitoring for misfires.

Both me and my buddies truck will show some misfires, mainly cylinder 8 at WOT and near redline. I’m not convinced it actually misfires as it runs perfectly under load. I went through swapping everything as well with no change. So I’m not convinced there’s an issue, unless it’s related to an airflow flaw in whipple a design. I have heard from people that when you get into boosted engines that misfire monitors can be slightly inaccurate.

Yeah, I’ve heard multiple people say they’ve had misfire thresholds modified in the tune. The misfire issue didn’t start until the whipple decided sucking oil was a fun hobby. But I wouldn’t disregard the air flow design as I’ve seen misfire from a handful of people with no primary cause. I’ve decided to leave the filter on the filler neck barb as a breather and the metco one with check valve in place for venting only. I tried to run it open and it got pissed off and threw a misfire code and a P0507 idle air control.