AOS Replacement

[vza]

Hi All, Replacing AOS 08 Boxster and cleaning out plenum and plenum tube. Is it necessary to clean the forward tube(closest to firewall). Seems like more of a pain to remove. I'm assuming most of the oil from the failed AOS is getting into the tube the AOS is attached to which is the rear tube. Thanks V

[JFP in PA]

Yes, the hoses are a pain to remove, but if they are not cleaned out, the car will continue to puff oil smoke until they are...............

[vza]

OK, So remove the forward most plenum tube as well? The rear was easy. The forward one isn't budging, does the intake manifold have to be loosened to get that off? I think there's a long AOS tube that disappears into the bottom somewhere.....what about that one?  V

[JFP in PA]

43 minutes ago, vza said:

OK, So remove the forward most plenum tube as well? The rear was easy. The forward one isn't budging, does the intake manifold have to be loosened to get that off? I think there's a long AOS tube that disappears into the bottom somewhere.....what about that one?  V

 

All of them.  This is exactly why it is a good idea to regularly check the sump vacuum levels with a digital manometer.  We always checked every car that came into the shop, regardless of why it was there; AOS has to be considered a consumable that needs to be monitored and replaced when necessary, like tires or brake pads, and prevents having to go through exactly what you are doing.

[vza]

OK, Any tips on getting that forward resonance tube off?  I removed the 4 hose clamps but it dosen't budge. V

Edited January 18, 2022 by vza

[JFP in PA]

These tubes take a heat set to the rest of the system and are not as flexible as they were when new.  You need to work with a hose removal spoon and free up the connections one at a time, they will eventually come loose.  In this weather, being inside a warm garage helps as well.

[Silver_TT]

17 hours ago, JFP in PA said:

 

All of them.  This is exactly why it is a good idea to regularly check the sump vacuum levels with a digital manometer.  We always checked every car that came into the shop, regardless of why it was there; AOS has to be considered a consumable that needs to be monitored and replaced when necessary, like tires or brake pads, and prevents having to go through exactly what you are doing.

 

This is worth repeating and applies to any modern engine that uses a PCV system as it is one of the most misunderstood topics.  In the case of the Porsche M96 design it is even more important since a bad AOS that isn't throttling vacuum levels to spec can literally suck oil into the intake and hydrolock the engine doing all kinds of nasty things.  Even in other designs there can be several modes of failure and the AOS is actually one of the most simple designs.  But some fuel and oil formulations can be hard on the diaphragm and they have also updated the material the diaphragm is made of to make it more robust.

 

I use a digital manometer periodically but I will still replace my AOS every 40-50K miles.  Too much to lose for a part that is a consumable.....

[vza]

Thanks....I got it all apart and cleaned. Now to get it back together!!

[Silver_TT]

strong work!