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Old 03-13-2015, 02:04 AM   #1
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Bench test an AOS?

So my resurrection project is nearing completion and I will be driving it to Hershey. I still have a funky idle - it drops to under 500 and hunts a little and then revs and drops revs and drops... I do see some smoke on startup and an leaning towards the AOS. I have 2 spare AOS's that were in the trunk when I picked it up. One has a cracked lower bellow still attached to it the other looks fine. Is there a way to bench test them? I searched and couldn't anything...

Thanks!
Mike

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Old 03-13-2015, 05:28 AM   #2
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I would pour oil into it. If oil comes out the bottom, and the air gets out the side vents, it's separating and it's GTG.

(Actually, any sign of oil on the vent tube means bad.)
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Old 03-13-2015, 05:39 AM   #3
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I would pour oil into it. If oil comes out the bottom, and the air gets out the side vents, it's separating and it's GTG.

(Actually, any sign of oil on the vent tube means bad.)
Sign of oil on the vent tube means bad means the AOS is bad or bad in another way?
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Old 03-13-2015, 06:36 AM   #4
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Quote:
Originally Posted by KRAM36 View Post
Sign of oil on the vent tube means bad means the AOS is bad or bad in another way?
I've read in a few places, and mine was the same, that oil on that top vent tube means oil has passed the AOS and its bad. I had puddles of oil in my intake manifolds when I pulled the throttle intake tube. AOS upper tube was oily.
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Old 03-13-2015, 09:27 AM   #5
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Originally Posted by Duquette5 View Post
So my resurrection project is nearing completion and I will be driving it to Hershey. I still have a funky idle - it drops to under 500 and hunts a little and then revs and drops revs and drops... I do see some smoke on startup and an leaning towards the AOS. I have 2 spare AOS's that were in the trunk when I picked it up. One has a cracked lower bellow still attached to it the other looks fine. Is there a way to bench test them? I searched and couldn't anything...

Thanks!
Mike
The unstable idle could be a dirty throttle body.
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Old 03-13-2015, 09:42 AM   #6
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While engine is running unscrew the oil fill cap, if you can feel a vacuum time to change the aos.


My moms 06 boxster sucked the cap down when the aos went.
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Old 03-13-2015, 04:56 PM   #7
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Mike,
A defective AOS creates an abnormally high vacuum in part of the crankcase ventilation system. This may cause a vacuum leak in tubes/connectors/pipes that may look perfect but have concealed defects. Try the old WD-40 test over the whole AOS system ?
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Old 03-13-2015, 05:17 PM   #8
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Some vacuum is normal on the oil fill cap. If you can test the pressure - normal is 5 inches. They say if AOS is bad then there is a ton of vacuum.

Also don't run the engine much if you can - they say too much oil coming from a failed AOS can ruin it.
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Old 03-13-2015, 05:40 PM   #9
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Slack Tube Manometer -at least 20" ?

In theory the vacuum is measured with a " slack tube manometer".
Perhaps someone has a diy? I found this but be careful you don't suck all the water into the engine!!!!
Homemade u-tube manometer - EcoRenovator
Here is the Pelican info:
Pelican Porsche Tech Article - Porsche 911 Air Oil Separator - Porsche 996 Carrera (1998-2005), Porsche 997 Carrera (2005-2008)
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Old 03-13-2015, 05:45 PM   #10
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Old 03-13-2015, 07:31 PM   #11
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Ive done the WD40 test and didn't find any other leaks. I didn't even think to try the oil fill cap. Was busy recovering the interior trim pieces today. Tomorrows to do list just got longer...

_Oil fill cap
_static vacuum test
_pull and clean throttle body
_Help fellow member wasateener pickup his newly acquired 2001 in CT
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Old 03-13-2015, 07:32 PM   #12
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Nice photo but without a brand/model, ........
Would this work?
PYLE Meters PDMM01 Digital Manometer with 11 Units of Measure - - Amazon.com
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Old 03-14-2015, 04:08 AM   #13
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Forgot to mention that it is also popping through the intake while idling. Im afraid to really let it idle to long to see if it clears up after warming up good. Once I do the oil filler cap test and pull the static vacuum if they are fine I may just let it idle for a bit.
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Old 03-14-2015, 04:13 AM   #14
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Oh and the trim work I've been cleaning up. All the parts that were covered in the peeling rubberized crap are getting redone:
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