Frequent blue smoke on startup and Motorsport AOS? UPDATED...

Hi all and Happy New Year! I have a question, on start up (everytime) I get a puff of blue smoke from the LHS exhaust. This never happened up until about 2 months ago when I had a compression test done and exhaust clamps replaced as they had corroded. The compression test was because I wanted to make sure my oil usage (1 litre/ 1000miles) was not due to any seal problems, all compression values are well within tolerance. I'm thinking the start of consistent blue smoke is just coincidence with the compression test...? Anyway, I've got oil residue on the plenum body, mainly LHS. All pointing to faulty AOS/ VOS. Would this cause the blue smoke on start up, back pressure sucking oil back into chamber when stopping engine? There's NO smoke under load or WOT and clears after 1-2 minutes, it's really just 1 big puff, and 100% blue, not white. Also has anyone replaced the stock AOS with the larger motorsport version, part number 996 107 926 00? Is it a straight swap, you don't need extra pipe work as Suncoast sell it with a pipe? I do aprox 5-10 track sessions a year... Many thanks,

Although the AOS primarily known for sending out clouds of white smoke, I've seen blue smoke too. With oil in your plenum I would just replace it with the $110. OEM unit. I'd be awfully surprised if that doesn't cure the issue. The dual chamber Motosports AOS costs in the vicinty of $600 and is overkill for a street car driven occasionally at the track. It was originally designed for cars competeting in the Grand Am Koni series where they would occasionally experience hydro-lock costing them a new motor. IIRC it won't fit in the 3.4's....

Thanks for the quick response. Mine's a 3.6, I'm just thinking that I'm not doing the DIY (read up on it and it sounds a PITA) so if I'm going to pay the 5 hours labour or whatever it is I might as well pay extra for something which will outlast and outperform the stock when I need it to??? I will be doing Spa weekends, Nurburgring weekends, and plenty of DE days in 2011...

Remove the throttle body. Check for evidence of oil wetness on the TB and its butterfly valve. If there is any... AOS is highly suspect. Check the area where the hose from the AOS connects to the intake manifold. If any oil puddled/collected there.... AOS. With the TB removed see what you can see in the manifold. If the manifold walls have signs of oil wetness... You know what. Another check is with the engine running unscrew the oil filler tube cap and see if you can remove it. In some failure modes, the AOS causes the engine crankcase to run under extreme low pressure to the point the pressure difference makes removing the cap difficult even impossible (unless you're Superman). If the AOS is original or a replacement and has some miles on it (50K? 60K? or more?) you might consider replacing it just in case. BTW, the compression test while the numbers were good doesn't mean the oil rings are any good. Just that the compression rings and the cylinder bores and the head gaskets good. All nice to know to be sure. Also, the compression test can't tell you if the valve stem or guides are worn or of the valve stems seals are leaking. These can allow oil to enter the combustion chamber and make smoke. The high oil consumption suggests that the oil control rings or the valve stems or guides or seals are passing some oil. But eliminate the AOS first as a suspect. Even if the oil rings or valve stems/guides or seals the source of the oil smoke you can run the engine a long long time before you need to take care of these items. Sincerely, Macster.

Quotes source post: 8174681

yea, @ $7/quart it takes a lot of quarts to get up to $15k for a rebuild - my guess is rings and/or valve seals

Could also be regular symptoms but cold weather gets you cranking longer with more fogged gas going out the exhaust after a labored start. How long is the crank and before the engine runs good? Cold weather and fuel injection used to be a curse. I hope its no biggy.

Quotes source post: 8174728

+1.... If it's coming from the aos, why would it smoke on the one side consistently. This will usually result with smoke with both exhaust.

hate to ask.... what brand oil and how frequently is it changed? also weight of oil

G'day Stuart, The fact that you get the smoke every time and only from the LHS makes me think its less likely but not impossible that the AOS is the culprit. I did have a bad AOS on my 996.2 and that would smoke every start at track days or after a spirited drive but it wouldn't smoke after 'normal' driving. Whenever it smoked it was always from both sides. A different failure mode could lead to different symptoms of course.

"1 litre/ 1000miles" Is that normal? I would say that mine 996 2002 uses max 2l in 6000 miles, and I too drive my car hard..

Thanks Guys. Only slightly longer than normal but still starts fairly easily, no labored crank, engine runs 'clear' within 1-2 minutes. No other symptoms. I'm using Silkolene ProS 5W-40 and I change at every DE or 5k miles, no problems with oil in that sense. I read your reports on that and the fact that it smokes from 1 exhaust is slightly confusing, there is a very small puff from the RHS but much less than the LHS. I usually take it for a spirited drive when ever I can and if I start her up within a couple of hours after then there is no smoke. It's only after it's been sitting for a day. Hence my thinking and going by Macsters explanation maybe it's during this longer sitting period that the oil mist in the inlets has time to 'drip' back into the chambers??? The oil on the plenum outside wall is definitely mainly on the LHS, could this be spray from the faulty AOS, a small crack in bellows??? I'll check the running with oil cap removed later today. According to Porsche you can use up to 1litre/1000KM (or 621miles) so I'm within tolerance. This has been confirmed to me by Porsche. The oil usage has stayed continuous since I bought her. She gets driven 'enthusiastically' with a proper warming up period. Oil gets changed very frequently (last year she had 5 oil changes). Previously she might have smoked 3 times in 2 years (including after DE), now it's every time she's been sat for a day or longer and it suddenly started happening in the last 2 months. I'm just trying to figure out why before I put her in for a costly fault find... Thanks again.

Your description of the issue does sound more like valve stem seals (oil leaking past them after an over night sit). Sounds like a good question to ask Baz Hart with respect to how common the issue is. Two other tests that can indicate valve stem sealing issues are (1) to see if there is a puff of smoke after the car has been at idle for a couple of minutes and then you pull away (2) Let the car roll down a steepish hill in low gear (no throttle hence with the engine doing the braking & high vacuum) and then accelerate away at the bottom and see if there is a puff of smoke.

it is possible that changing brands of oil might have some effect - we run a lot of oil threads here and on the 911 board where people find switching brands makes an unexpected change - sometimes for the better, sometimes for the worse...its just a thought

Quotes source post: 8175739

I'll try those next weekend before taking it to the shop. In the meantime I'll try mailing/ calling Baz, problem is he's pretty far away from me. I took the filler cap off whilst engine running and no problem there, easy to get cap off and mild change in engine running before settling. I changed from Mobil1 to Silkolene after a lot of research and recommendations. Even going to a 10W-50 during the summer season as my oil pressure was 0.8-1bar at hot idle after back to back 'Ring laps on 5W-40. Last change was back to 5W-40 for colder starts and season end.

good lord you are driving on the ring... I would give you a few quarts if I can come (what a dream that must be!)

Quotes source post: 8176401

You should fly over and rent a car, plenty of companies around that do it, seems a lot of the US guys are doing that now. I'm staying away from the standard Tourist days now though, it's just too damn scary with all the bikes about. Sticking to closed events now...

Yea, I watched some vids and thought "HOLY CR@P" not interested in getting killed!! good idea on closed days

Quotes source post: 8175734

Like Macster says the worn valves stem guides and seals cause oil into the cyclinder after sitting. It burns off after starting. Just try holding paper at the exhaust to see if the paper has oil on it or more of a fuel smell. During the 1-2 minutes is the engine running strong with no stuttering? You say it all started after the compression check so I'm thinking maybe a center condutor of a plug had a seperation or the tip of a plug or two got dirt or knocked out of specs when being moved around. Plugs center cores take some major heat and become brittle in there. I'm sure prosches 100k miles life span of a plug doesn't fator handling them. Anyway maybe try new plugs on at least the troubled side. Beats tearing the engine down Pay attention to which cylinder each plug comes out of to diagnose which cylinders to keep an eye on. You can find pictures online to diagnose looking at plugs tips. Oil generally leaves the plug dirty and some time still oiled up

Quotes source post: 8176590

It does stutter slightly until running clean, but only very slightly. I started her up earlier and watched round the back and you can definitely hear a stutter of sorts. I'm taking it back to the place that did the compression test. It's just weird that all this happened right after they did the test. It had new plugs 9k miles ago. So can a plug cause the settling of oil and then smoke? I'll ask them questions regarding this. Thanks.

Quotes source post: 8175523

Not necessarily. The hose that runs from the AOS to the intake manifold can end up depositing most (if not nearly all) oil on the intake walls that favor one cylinder bank over the other. At least this is true with the AOS and intake system of my Boxster. I have not been that up close and personal with a 996 engine's intake system and AOS though. But if I'm right, in this case the smoking can be light to non-existent from one bank and of course heavier or only from the other bank. Sincerely, Macster.

Quotes source post: 8176590

That is a very smart observation regarding the compression test and plugs. Last thing touched... If not a plug then possibly a coil was not installed properly or could even be bad? Sincerely, Macster.

Macster I've got the deep laugh anguish in my mind after reading what you said. I remembered the the good old days and how if you are around long enough in cars you find some mighty percular things to remember when diagnosing. More to the point of the deep laughing anguish feeling that overcame me. I'm sure you can remember some times of old where a buddy you hotrod with or others have gotten the firing order wrong when reconnecting the spark plug wires. I didn't think of it at first but it just came to mind. The car can seem to run ok with two plug wires reversed but it does run a lot better wired correctly. Just another of the many things that can be checked.

Thanks guys, will be on the phone to Porsche tomorrow and get it booked back in and have them check their work and possible AOS.

C'mon Dervish....what was the final outcome? You're keeping me in suspense as I have the same symptoms!

UPDATE: Well I went to get the low temp thermostat fitted (as per LN Engineering) and the specialist doing the work would rightly only fit after sticking a camera into cylinder 6 to check for health. Diagnosis was scored cylinder! Long and short of the story meant new engine or rebuild. The specialist www.hartech.org is a very well respected Indy with by far the greatest watercooled R&D in the UK. We agreed on the rebuild route with modifications to try and prevent any future problems. The list being: Overhaul cylinder heads (skim, de-coke heads & valves, re-lap valves to seats). Re-build with new gaskets/ seals, new modified IMS bearing and spindle, new crank shaft oil jets, crank shaft bearings (big end, main & thrust), timing chain set & 2 guides. Lower temp thermostat, modified cooling channels, new graduated head gasket (as 3.4). Anyway, she's back with me now and I'm glad to say there's no smoke on start up anymore!

WOW what an update. Bill must of been expensive for all that!

Quotes source post: 8551230

Just over 9000 of our finest English Pounds! (20% Tax f'kn UK government!!!)

wow.... what causes a scored cyl? You'd think everything will go through the air filter. Thanks for the update Dervish.

sorry if i missed it, how many miles did you have on it?

The scoring is the result of poor design, simple as that. The 3.4 engine has graduated coolant channels, getting larger as you go around the engine from cylinder 1 to 6. On the 3.6 the channel and gasket holes are all the same size, resulting in cylinder 6 not getting as much coolant flow as 5 which doesn't get as much as 4 etc etc etc. The scoring is evident on the thrust side of the piston where the heat is greatest. I'm massively over simplifying things but that's the idea. It's all here for reading http://www.hartech.org/docs/buyers%2...20part%205.pdf There's a lot of info but 3.6 owners should seriously read it. And for the record I had 51000 miles on the engine and was religious about oil changes, every 5k miles, and always warmed the oil (not water temp) fully before driving hard.

Quotes source post: 8551685

I just finished reading the article and it's shed some more light on these engines for sure! I'm going to check the rad fluid and possibly change it, and do the rad cleaning very soon.

Just keep driving it until she's dead?

Quotes source post: 8175739

Hi I am having similar issues with my '08 Cayenne; a cloud of blue smoke on startup and stuttering and puff of smoke after the car has been at idle for a couple of minutes and then acceleration away. Also when I slow the car down a hill in low gear (no throttle hence with the engine doing the braking & high vacuum) and then accelerate away at the bottom and there is a puff of smoke. I have changed the AOS last weekend and new spark plugs but not much change. the first two plugs were black with carbon n oil build up. Oil consumption is high.. 100K on the clock i'm starting to think its some engine seals? I only have her 3 months too, bought from a dealership...purchased an after sales warranty with first warranty group. Any advice would be appreciated

sounds like scored cylinders. get the cylinders scoped. Cayennes do score, probably not at the frequency the 996's do

Quotes source post: 14138369

thanks. How do i go about getting this done? Is it expensive? if that its the problem its prob a total engine rebuild right?

I don't know how labour intensive it is as I never worked on one. But essentially they use a small camera to access the cylinder to take a look at the walls. on most vehicles, it can be done by removing the spark plug and going through that way. you can't fix scored cylinders without opening up the engine. You will get better answers in the Cayenne forum!