Dharn55

When I reinstalled the engine in my 2000 996 after fixing the intermix problem I also installed a new AOS. No problems until recently. I had to replace the starter motor a week ago (always something). AFter replacing the starter when starting the car there is a tremendous amount of smoke which goes away in a short time. I am thinking that I knocked something loose on the AOS. I removed the throttle body and there is a thick film of oil inside the plenum. Seems to be coming from the breather tube that I believe comes from the AOS and attaches to the plenum. Any ideas on what might have come loose?

Macster

Not too many things to come loose. Time to give the AOS a good once over inspection looking for any loose connections, cracked hose, etc.

Not 100% positive but excessive smoking not a typical sign of a loose AOS connection of some kind. A bit of an oil leak or symptoms of a vacuum leak are signs of a bad or leaking AOS connection.

Excessive and prolonged smoking upon startup is almost always a symptom of a bad or going bad AOS. It is not impossible the new AOS has gone from new to bad in a short time. Rare but a new part/assembly can fail early.

Another source of the smoking is an engine overfilled with oil.

Sincerely,

Macster.

jrgordonsenior

I've recently researched the AOS for these 3.4 motors as I just started racing one. I originally was going to install the dual chamber Motorsports unit that is used on the 3.6's, 3.4 S's, and Caymans but I was told it doesn't fit the older 3.4's. Since that unit costs around $600., I didn't chance buying one. Instead I took a new OEM unit and vented it to a catch can rather than to the intake. You have to block off the intake of course and I doubt this is a good fix for a street car, but it works well for a race car...

I've also been told it helps to let the motor idle a minute or 2 before shutting it off. The AOS gets overwhelmed in heavy braking and turning, so presumably letting it idle allows it to slowly cycle out the heavy vapors. I would give that a shot first and then replace the unit if that doesn't work. It's too bad the 2 chamber unit doesn't fit....

Dharn55

The stange thing here is that there was no smoking until I replaced the starter, also jacked the car up to put one of the shifter cables back into the holder. Then started it up an lots fo smoke for 15 seconds or so. Did not add any oil and the guage and dipstick don't show an overfill. The inside of the plenum and the intake runners are now thick with oil, and it seems to be coming from the breather tube to the AOS, only real source for it up in the plenum. Hate to think that the AOS went bad as these are extremely hard to get at with the engine in the car. Maybe when I had the rear of the car jacked way up to slide under it to get at the shifter cable some oil flowed into the AOS and will take a while to filter out. I can't remember, is there a vacumn line that connects to the AOS?

Macster

Hard to believe jacking car any could result in any oil into intake. These engines are designed to deal with very high g-loads and still keep oil in the engine where it belongs.

AFAIK the AOS is way above the oil level of the crankcase. The AOS is designed to route crankcase vapors through its interior chambers that contain tight turns which cause the heavier oil particles to leave the air flow and contact the interior walls of the AOS and these walls are designed to let the oil on them drain back down into the engine.

The crankcase varpor after it has gone through the AOS is then routed to the intake manifold right behind (at least this the case on my 02 Boxster) the Throttle Body. When the 1st AOS on my Boxster was acting up -- though at the time I didn't know this was the problem -- the opening of the hose connector the hose from the AOS connected to right behind the TB was very oily with oil on the TB and even its butterfly valve.

In short I'm having a hard time imagining how a properly functioning AOS could account for that oil in the intake manifold. The AOS is not designed to accumulate oil, but to as I mentioned above separate the oil from the crankcase vapor and return the oil -- via gravity -- to the crankcase and engine oil sump/reservior.

If the engine not overfilled with oil and though highly imporobable but I mention it to cover all bases if all of the oil scavenge pumps working properly then I'm still fixated on the AOS as being bad, or going bad.

But first, it is possible to under some situations to overwhelm an AOS. Some function better than others and some engines generate more oil vapor in the crankcase than other engines. If the AOS not one of the better ones at removing oil vapor and if the engine a bit of an oil vapor generator it could be some quantity of oil is going to get past the AOS and make its way into the intake manifold.

Once there the engine will smoke until this oil drains down and into the engine's combustion chambers. If the oil dosage from a less efficient AOS and a heavy oil vapor generating engine gets to the intake manifold's walls and TB and of course all surfaces between the AOS and where the hose from it connects to the intake manifold it can take some time for the oil to go away. Thus almost every time the engine is allowed to sit and then started it will smoke upon startup.

With engine up to temperature and idling how's the vacuum at the oil filler tube opening with the cap removed? Can you remove the cap with the engine idling?

Also, a bit of work but you can remove the TB and clean it and the connector where the AOS connects, wiping away all traces of oil you can, then buttoning everything back and running engine for a while. Nothing fancy or exotic, just normal usage. Then when cold removing TB and looking for signs of fresh and heavy oil coatings where you cleaned it away before.

If oil coating heavy.... AOS is again suspect though I'd be darned sure all hose connections to the AOS are correct. I'm no AOS expert but I wouldn't be suprised to learn hooking one up wrong might account for the symptom of heavy smoking.

Sincerely,

Macster.

C4CRNA

I think you have to look at it's somethng you loosend when you did your recent repairs.
Something got pinched or moved.
I know it sounds farfetched ,that has to be it.

C4CRNA

Any update?