check this aos thread out ...
 

check this out ...

guy on rennline 996 forum calls himself 'porschetech' has developed a mod where you deactivate the aos by blocking the reference air vent such that the diaphragm doesn't move. asking people to pay $10 to the 'porsche gods' (his paypal address) for the instructions to block the vent. folks lining up with chequebooks in hand and a glass for the koolaid ...

https://rennlist.com/forums/996-forum/1176175-the-ultimate-aos-solution.html

so, less than two weeks later and 135 posts. he has 'diy licenced field testers" (the guys that paid $10?). it appears that he has now incorporated an aftermarket aos diaphragm (probably realised the original one was there for a purpose; sorry didn't have the self-control to read the entire thread). appears to be the same one that raby tried and didn't use because was too big - allowed to much vacuum on crankcase at idle causing overrev as engine drew in combustible vapours.

lol, 10$ a god! what a prank though :/

You should read the thread.

Seems like a solid solution and Jake Raby chimmed in. Only reason he didint get involved was to not get destroyed by the EPA, not because it wasnt a good solution.

Keeping an eye on it.

I really can't bring myself to read 17 pages of thread..... can you nutshell for us?

Reading the first page and the last page, it looks like this has turned into something yet MORE convoluted and complicated than the AOS, but maybe there's more to it? (Or less, Haha? )

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i did. i also read the links in the thread, such as this one:

https://rennlist.com/forums/996-foru...l#post14198625

where jake says:

-The AOS balances fuel trim. If the pressures are not correct within the crankcase the engine runs rich, or lean, and that means an AOS can kill cylinders, create oil consumption, and etc.

there are other threads on the issue where jake specifically says that he was unable to fix the fuel trim issue with other aos units. and this is a guy who actually builds and tests these engines, not a self-proclaimed 'porschetech' and 'porsche god' that is selling $10 licences to people to do his testing for him.

basically, what is happening is that the heat and churning of the oil in the crankcase creates vapors which in turn pressurize the crankcase. if unaddressed, this pressure blows seals, pushes past piston rings, kills engine power as it resists the movement of pistons.

this vapor cannot be vented to atmosphere by law, and is combustible given the oil content. the aos uses intake vacuum to evacuate the crankcase and reintroduce it into the intake.

the thing is, most of the vapors and pressure are happening at high rpm, while most intake vacuum is happening at idle. this is why there is a diaphragm on the aos. at idle and high vacuum, the vacuum draws the diaphragm closed and restricts flow from the crankcase. as vacuum decreases the diaphragm relaxes and flow increases.

this diaphragm flaps in and out a bazillion times and is a failure point. when it fails the intake is applying full vacuum all the time; this is why a bad aos is detectable at idle by difficulties in opening the oil filler cap due to the increased vacuum at idle.

the issue is having an appropriately-sized diaphragm. too small (or open too slow) and not enough vacuum is applied at high rpm, not enough pressure is relieved, power is lost, seals and rings fail.

too big (or close too slow) and when you come off wide open throttle all the vapors get drawn into the intake and you get more fuel (oil vapour) than expected creating an over-rev situation.

the porsche god appears to be evaluating the replacement aos diaphragms by durability and not response to vacuum (other than a few static vacuum measurements that do not give any indication of the dynamic response of the diaphagm).

having said all that it work fantastic on his car, apparently.

You might be surprised at how many shops get "visited" by federal emissions and safety nannies. We were visited more than once over everything from emissions to potential liability claims, and we came up clean every time. Major pain in the butt when you are running a business and have to stop while they rummage through your computers and records. I still probably get two or three requests a month about how to turn off TPMS systems (yes, there is a way, and no, I will not tell you how to do it).

The government knows that specialty shops are the major source of methodology to circumvent these systems, the potential revenue stream simply does not cover the grief involved.

aos vents the crankcase and heads for reasons detailed in my other post. body of the aos is a swirl chamber designed to separate the liquids from the vapors. the 'head of the aos' is the diaphragm noted in my other post. the diaphragm connects to the intake.

aos diaphragm can break, failure can be catastrophic if your engine ingests oil and hydrolocks, aos is hard to get at and replace.

the porsche god is keeping the original aos in place, disabling the diaphragm in the aos (blocking that vent) installing a replacement diaphragm (a vag piece) in an easy to service location and adding a catch can with a sensor as a failsafe.

Aaaahhhhhh. There's the peice i wanted to get to.

Interesting approach, I guess.
I'm only mildly and peripherally interested, since my own solution seems to be working quite well.

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it's a great solution if there were certainty re the replacement diaphragm; inexpensive, uses off the shelf parts, etc. (catch can is the exception, but that part is optional i would suggest). i just don't see the certainty there. and to take (give) money without the proof seems a dangerous combination of vanity and foolishness.

It is only 10$ on a 911 forum :).
The price of a fancy pint of beer with tip.

The guy seems like he's retired and used to be a FoMoCo troubleshooter. Seems to know his ****************.

Indeed, using an off the shelf diaphragm, that does the regulator part, leaving the original AOS there for the vortex part, blown or not blown.

Just that is a solution to not have to remove and mess around with the AOS anymore.

His can with infra red warning, is just a nice to have for early warning.

Its interesting in any case.

@Maytag Which was the solution you ended up going with?

Interesting tread, interesting approach. If I understand correctly, this guy didn`t do anything but made the AOS membrane more easily accessible. How often do you have to replace the AOS anyway?

Mine went out after I'd owned the car for 20k and about a year.

I don't get the "solution". Its not too terrible to replace the AOS. You do kinda cut up your hand a little on that top engine bay area, but if it fails at most every 20k its not like the end of the world. IIRC rock auto had it for like $40 or something; so it wasn't really expensive either.

I'm anticipating an AOS replacement sometime soon. Which one did you go with? The SKP or the URO Parts?

Yeah, I don`t get it either. I`ve read somewhere here that the original AOS lasts much longer than the aftermarket ones. The genuine units sell for around $100 on ebay. My car I think has the original and has 100k in it. I put 100k miles in our family car in about 10 years, and this is a fun car for the weekends for many of us, so what`s the big deal?

Gents, replacing the aos on a 996 is a much bigger and more challenging job

Yeah, its in the way back on that one. Oddly the mid engine car is easier to work on in this respect.


I want to say I did the uro brand. When I got the car the first thing I did was replace like all the coolant hoses with that uro brand; and I felt their quality was good enough with the hoses.

Thank you.