Macster

The engine sounds normal. A bit of valve clatter/chain noise at cold start but there's a lot of valve hardware and chains in that engine.

The smoking... The techs tell me they see this all the time, with customer cars, used cars, even new cars. (When I was looking at a new Boxster (the one I eventually bought) it smoked upon startup. 305K+ miles later it still smokes upon cold start a few times between its 5K mile oil/filter changes.)

The guidelines are as long as the smokng is brief, only occurs when the engine is cold, the engine exhibits no untoward behavior, the CEL remains dark, there is no problem.

The oily plugs on the one bank suggest oil is getting into the engine. The most common path is via the intake manifold and this oil comes from the AOS.

If you want to have a professional Porsche tech listen to the engine and give his opinion that's a good idea. In these cases I recommend this. The tech's the professional. He's at the car. He can offer the opinion with the most weight.

Bradstock

Thanks Macster, I appreciate yours and the other opinions, and agree that there is no substitute for diagnosis from a pro. I'll be making some phone calls, making a decision about where to take it, and will take it in this week. I'll keep you all posted.

Bradstock

After a bit of research, I think tomorrow I will call Hergesmeimer in Lake Forest and possibly one or two others to get their feedback and take it in for diagnosis. In the meantime, it's Sunday and I'm bored so i'm poking around myself … it might just be me but I don't hear any weird engine noises; here's a short video I took of today's cold start, with the phone closer to the engine:
Again aside from a few seconds of smoke which only appears on cold start, there are no other issues, no leaks, no lights, no sounds etc.

Schnell Gelb

It is "Hergesheimer" Motor Sports.
If you dig you will find some negatives. That is why I did not mention them even though I realize they are close to you.
There is a rattle at .06 &.07. But much briefer than before.

Flat6 Innovations

I'd not jump to conclusions on this one.. the AOS could be getting weak, or you could have a bad injector that's sticking. Bad injectors allow fuel to dribble after the engine shuts off, and at start up this creates smoke..

I am seeing more injectors cause cylinder failures today than at any other time. When the engine smokes it looks just like (and smells like) oil smoke... why? The excess fuel washes the cylinder down and pulls oil into the combustion chambers where it is burned.

Bradstock

Nice of you to jump in, thanks. Again the AOS was replaced about 1000 miles ago, but the injectors were not something that has been mentioned or something that occurred to me (or even mentioned by my local shop). I'll be bringing it to a reputable shop this week and will be sure to ask about the injectors.

Flat6 Innovations

New AOS doesn't mean it's a good AOS. One of the parts companies I do development for recently shared with me the return percentages they have for the AOS units for your generation of 996, and it was staggering.. I have had several bad units myself, one must test the AOS with a manometer evaluation after install, else you may have a bad one and think it's good... only because it's new.


There's a good possibility that none of the shops you deal with have heard of, or would even consider the injectors. This is something that afflicts the M96, and at a specialty level we connect the dots.

Go see Tony Callas... there's a reason why we instruct classes together... We'll be doing another M96 class together, this week.

Bradstock

Very interesting, thanks. I was aware that there is a significant defect rate with new 996 AOSs, and even brought that up to my local shop. They replied that upon inspection, the new AOS was not oily, so they assumed it was working fine. Rennsport Torrance has an excellent reputation, but it is a bit of a haul. I will probably start by discussing the issue with closer reputable shops like Hergesheimer, but if they are not familiar with the issues you are discussing, I'll head up to Rennsport.

Flat6 Innovations

There's several ways that an AOS can fail. An external leak is only one way.

Of all the units I have had fail out of the box, only 1 had an external leak.

Tony Callas developed the AOS test using a manometer for these engines. He also developed the tool to carry out the evaluation.

Bradstock

This morning I spoke with Robert at Auto Strasse in Costa Mesa (recommended by a good source) and Mark Hergesheimer at Hergesheimer in Lake Forest who also comes well-recommended as being experienced with 996s. Both seemed very knowledgable and agreed the new AOS could be at fault, even if its not oily (although upon checking today there's no real vacuum when removing oil cap at idle for what that's worth).

Mark Hergesheimer asked me how much I have driven since the AOS replacement, and I see that I have only driven 600 miles since it was replaced on 8/31, and that I have lost only 1/3 qt or so. Interestingly, he asked how hard I had driven it since, especially regarding cornering. He said there are places in the engine where oil from the old AOS can get stuck, and it can take quite a bit of spirited driving (especially in corners) to burn it all off. Absent any other warning signs, he suggested I drive it more with the hope of burning off the residual oil from the old AOS, and see if I notice any puffs of smoke upon cornering while accelerating.

Based on all of the information I have right now, I think Ill take Mark's advice and drive it for another month or two, giving it some more acceleration especially during cornering where safe. If nothing changes in the next couple of months (or if any new issues come up), I'll take it in. If any of you agree (or think I'm an idiot) feel free to speak up. And again thanks for the comments.

Bradstock

Update: 11/2: This mystery is bugging me, so today I found a more capable Porsche shop nearby who knows the M96 motor. The owner attached a manometer to the oil filler cap and found that the vacuum was about 3.5 (a bit less than the recommended 4-7 level but not quite enough to throw a code), which could explain the cold start smoke. He suggested that the AOS could be the culprit, but that the next step is that tomorrow he will attach a smoke machine to the dipstick tube and see where the smoke escapes from, which will hopefully get us our answer. If the AOS, I will go back to my local shop for replacement.

Smoke test will be tomorrow. Stay tuned.

Schnell Gelb

Great transition from speculation and keyboard mechanics to real diagnosis.Well done !
There are several common leak points that the smoke test will confirm/eliminate.Some are unrelated to your symptoms but are useful anyway - for example cracked AOS tube, cracked oil filler tube,disconnected vacuum hose.
Video the smoke test and show us?

Flat6 Innovations

This is exactly what should have been done, and the only way it should have been done. Its what I would do.

This is the only way to scientifically perform this test.. Sound like he's attended the classes that Tony Callas and I instruct.

Bradstock

Haha thanks. I'm beginning to see a dysfunctional pattern in these forums which I fit nicely into (likely the subject of an upcoming post topic I've been thinking about).

I'd love to get video of the smoke test to post for everyone's edification, but I don't want to be the overbearing repair shop customer. Not sure what the protocol is. In any case, I'll let you know the results tomorrow.

Bradstock

Yeah,. It's tough to know what to do when faced with so many recommendations and so much uncertainty. It's a pretty wide range between "flatbed it to Rennsport ASAP" and " Drive it harder". And of course the easiest option tends to win, at least temporarily.