986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post

ike84 · 08-06-2021, 05:52 PM

It's 5 inches of water.

Most modern engines work on positive crank ventilation (pcv) in order to evacuate blow by fumes and funnel them back into the intake. As blue said, ours actually works in opposite to achieve the same effect, plus to seal the low pressure rings (although there are reports of running our crankcases just vented to atmosphere, which transfers them to a PCV system. But I digress ...)

This is a tiny vacuum. The cap should come off easily but you can feel a pull if you put your hand on it.

Slack manometer is the tool for measurement. This is one way to actually tell if your AOS is bad (AOS failure allows more vacuum pull of the crankcase)

The idle changes because the intake pulls on the aos, which pulls on the crank case, which communicates with the fill tube. Open the cap and you've essentially created a vacuum leak past the TB, letting in unmetered air and causing the idle to surge.

Sent from my SM-G970U1 using Tapatalk

08-06-2021, 05:52 PM	#169
ike84 Registered User Join Date: Oct 2020 Location: KY Posts: 1,214	It's 5 inches of water. Most modern engines work on positive crank ventilation (pcv) in order to evacuate blow by fumes and funnel them back into the intake. As blue said, ours actually works in opposite to achieve the same effect, plus to seal the low pressure rings (although there are reports of running our crankcases just vented to atmosphere, which transfers them to a PCV system. But I digress ...) This is a tiny vacuum. The cap should come off easily but you can feel a pull if you put your hand on it. Slack manometer is the tool for measurement. This is one way to actually tell if your AOS is bad (AOS failure allows more vacuum pull of the crankcase) The idle changes because the intake pulls on the aos, which pulls on the crank case, which communicates with the fill tube. Open the cap and you've essentially created a vacuum leak past the TB, letting in unmetered air and causing the idle to surge. Sent from my SM-G970U1 using Tapatalk __________________ 2000 Box Base, Renegade Stage 1 performance mods complete, more to come When the owners manual says that the laws of physics can't be broken by this car, I took it as a challenge... Last edited by ike84; 08-06-2021 at 05:56 PM.