I was Wrong - PCV and Fresh Air

[donjetman]

The PVC system does take in filtered fresh air. On modern fuel injected engines the source is from downstream of the MAP sensor.

On a healthy engine there isn't much blowby volume, so a fresh air source is included in the PVC system to help increase air flow volume to carry away harmful vapors from the crankcase.

He's a picture of my finger pointing at the fresh air hose on my 2002 LS1. Its connected to the throttle body and the valve cover. I haven't been able to determine if there is ever a vacuum on it, or if it's always has positive and/or neutral pressure?

 

[iamdub]

*PCV, and the intake is downstream of the MAF and upstream of the MAP

On a serious note and in a short answer, I'd say "yes."

 

[donjetman]

I meant to post this in the 2007 to 2014 area

 

[OR VietVet]

PCV=Positive Crankcase Ventilation

 

[Miami-Dade]

I meant to post this in the 2007 to 2014 area

MOVED YOU HERE.

Next time let a mod new. We can't be everywhere 24/7.

 

[j91z28d1]

back story?

but yes, my yukon has a air inline in the air duct after the maf before the tb. sucks air into the intake on the driver's side. I left the hose off the intake duct once and the fuel trims were off a lot, like over 10% positive at idle. I didn't stick my finger over it, but I would guess it's because it was sucking unmetered air thru the crank case into the intake, causing it to add fuel?

 

[Dustin Jackson]

I would hope that it would have vacuum from the intake unless its acceptable to have enough crank case pressure to push it the other way around

 

[j91z28d1]

I would hope that it would have vacuum from the intake unless its acceptable to have enough crank case pressure to push it the other way around

I think it's kinda expected or designed to do both. good sealing fresh engine should have enough vacuum at idle to handle the volume of blow-by passed the rings but when you go wot you have almost no vacuum in the intake, so at that point the blow by is being pushed thru the pvc system. I'd expect little bit thru what would normally be the suction side and thru the intake side. so you reburn all that emissions. and just raw gas smells of the old days.

that's why I kinda think you need a catch can on both sides, at least of a more worn engine used in a more performance application or at least driven hard like long tows up mountain at full power.

like say my yukon, probably not. I expect it lives most of its life under vacuum probably seeing half throttle once a month and it's surprisingly tight sealed engine for 150k compared to my c6 that gets fired up, beat on almost constantly at wot either track days or whatever I'm doing with it.. being it's got 110k and abused many times over my stupid mistakes and the seemingly random ls ac belt throwing issues, it could probably use a catch can on both sides.. but sadly it has none and the truck has one.

 

[gooffeyguy]

Yup, and that air is metered (located after the MAF)

 

[RET423]

The port from your throttle body to the passenger valve cover does not have vacuum, it is designed to use physics and act as a pressurized line pushing air into the valve cover.

If you look into the front of the throttle body you will see that this port gets access to the air stream at a machined flat area that faces the air flow. As the engine draws in air the flowing air hits that flat spot and bounces back, creating a mini high pressure system that uses the hose to the valve cover as an escape.

Without that machined flat area it would act as a vacuum port, but with that little flat spot it acts as boost.