2002 996 C4: Bore Score, Valves or?

So my 2002 C4 cab 6-speed with 42k miles which I've had roughly 5 months continues to emit 2-5 seconds of white smoke from the left exhaust on nearly every cold start. Had PPI plus compression check and leakdown test before buying which all passed with flying colors but did not pick up on this problem which again only shows itself on cold start. Changed AOS a month ago which reduced oil consumption considerably (I've lost little or no oil in the 1k miles since), but the smoke continued. I've seen some rennlisters say that some smoke on a cold start which resolves quickly and without other symptoms is nothing to worry about, but it didn't seem normal so I brought it back to my local shop (franks motorcars in Laguna beach) to look again. Replacement AOS seems fine but plugs on the right side are oily when pulled. They say boroscope won't give a clear enough view for diagnosis, so they recommend pulling the engine to see if the problem is valves, cylinder scoring etc. They said if it's valves then we're looking at $3700 valve job, but if it's something more serious like so cylinder scoring , we are looking at a $7000 short block from Porsche, plus around $6000 in additional parts and labor, plus tack on another $800 or so if I want to throw in a new clutch (Around $14,000 and two weeks all in). By the way, I hear no clicking/tapping noise from the engine which I know can sometimes indicate cylinder scoring. Aside from the money, it's a bummer to think that the previous owner probably had some idea about this problem and decided not to mention it. Anyway, I'd appreciate any thoughts and advice, as well as recommendations of any other shops in orange county CA which you feel would do the best job diagnosing and repairing this. Thanks, Brad

No need to pull the motor yet. Scope from the top, then pull the oil pan and scope from the bottom. If your bores are scored, one of those will see it.

Yes I agree with gnat, it won't be valves if your getting smoke it will be a cylinder just remember which ever tailpipe you get the smoke from it will be the opposite bank you need to check as the exhaust passes from one side to the other so if you look at the rear of the car and the right tailpipe is smoking it's left bank 1-3 and if left is smoking it's right bank 4-6. You can get smoke on cold start from condensation and also from cold fuel map settings but really you should see the same from both banks, if one is more than the other it could be a problem but this can be identified without getting committed by borescoping like gnat said, and it should be a relatively small cost , you could do it yourself if you have some knowhow especially from the bottom where you are most likely to see scoring as from the top it is often hidden by the piston itself as even at bottom dead centre the piston is still covering the bottom part of the cylinder. Basically drain the oil and remove the sump plate, place the piston you want to look at on top dead centre and put the borescope in. I'm sure others will chime in, post a video of the smoke if you can!

No CEL. No noises. No other symptoms. No signs of any engine trouble just a brief bit of smoke upon startup. No problem. Relax and enjoy the car.

"The plugs on one side oily" multiple oily plugs are less likely to be bore scoring then something else common to one side. I tend to go with Macster, drive and enjoy it. At least until more symptoms show up. As an aside, I have a, new to me, Turbo that randomly (hot, cold, sunny, cloudy) smokes a good puff on startup. I found that if I keep the oil between 1 & 2 bars low on the indicator it does not smoke on startup?? Turbos have a true dry sump engine so why would ~1/2 quart make a difference? I don't know and it is not going to stop me from enjoying the car.

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My guess is the oil level has nothing to do with the smoking on startup. What you are probably seeing is from a leaking turbo seal. Do you let the Turbo engine idle ~2 minutes before shutting it off?

The OP says all three plugs on the right side are oiled . Odd that all 3 are oily. So logically the cause is common to the entire right side bank. 1. all 3 cylinders are scored/cracked - strange coincidence 2. all 3 have worn oval -ditto 3. all 3 have badly worn oil control rings, suddenly and simultaneously 4. all 3 have simultaneously worn valve stem oil seals or valve guides And none of this was apparent in the PPI ! Weird.Sounds like my experience all over. Time to visit Tony Callas at RennSport,Torrance for a diagnosis ?

Hey everyone,Much appreciate your insight and suggestions. I just spoke with Franks motorcars again, and they confirmed that all three spark plugs on the right side were oily. For the person who asked for a video of the smoke, it's here:https://youtu.be/8WKi3oKwFpY for further diagnosis, I'd rather an expert look at; I'll go to Rennsport in Torrance if necessary, but something closer to South Orange county would be a bit easier; any suggestions? Regarding the suggestion to just continuing to enjoy the car since there are no other symptoms or error codes, judging from the amount of smoke in the video I posted above, how bad do you all reckon this is for the engine? My gut feeling is just to bite the bullet now and fix it, but if there's a good chance it could just continue like this for years, I might wait a bit. Such a shame because I was very picky about using a car with low miles and excellent condition, there's barely a scuff anywhere inside or out on this car. thanks, Brad

Sorry, the smoking video is here: You Tube

From your video, in addition to the smoke, there's a really loud and bad knocking noise when the engine is cranking. I suggest not to drive it much until the problem is diagnosed.

I agree, I am more concerned about the brief knocking. It 'seems' as if it is slow to build sufficient pressure/volume to cushion a worn bearing or pump up something else.I am not going to speculate but I think many of us can guess.Which is exactly why you shouldn't listen to us -they are guesses! Diagnosis is the most crucial and valuable part of this. Some can repair the M96, few can do the diagnosis as well as Rennsport. Yes they are not cheap but an inaccurate diagnosis will be a very expensive mistake ! The flat bed will cost you more than the diagnosis. Savings can be made elsewhere perhaps but a cheaper diagnosis .......... Ask local PCA for recommendations ? There are M96 repair places like 9XX Motors in LB and his buddy UFO in GG or Auto Strasse in CM - but first you need a diagnosis. Be prepared to be given a list of possibilities with probability and cost for each. Once a mechanic starts tearing into the engine you are trapped.

Thanks guys, do you hear the same sound in this video taken a few days prior? You Tube

Nope ! Flatbed before you do more damage.

You need Jake's golden ears.

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No just about 45 seconds, 5 to 10 of which is oil level read time.

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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.

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.

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: You Tube 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.

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.

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.

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.

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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.

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.

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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.

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.

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.

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?

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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.

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.

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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.

"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. " Wow, that would be FREE advertising on Rennlist in a Thread where Raby says it was the correct diagnostic procedure. You would be doing the Indie a great service to offer such a video posting. That kind of validation is hard to come by .But O.K.

I'll explain the situation to the mechanic and see if he's cool with me taking and posting video. If so, you'll see it tomorrow.

We need to give competent M96 mechanics all the support we can ? They are few and far between and we need them !

We may have given all kinds of crazy ideas, but the key part that everyone seems to have agreed on is that the idea of dropping the motor at this point in time was ludicrous. Far too many other avenues of investigation were available. Glad it's looking like something simple even if it is annoying.

Update 11/3: The mechanic who did the manometer test yesterday performed the smoke machine test today which found a small leak caused by an improperly-installed (Fabspeed) intake hose clamp. Replacing this brought the vacuum test result up to 4 (acceptable range being 4-7) so that issue is solved. He then inspected the AOS which he confirmed is a good OEM part and installed correctly with all hoses etc.. intact. He then inspected the intake and found that oil is pooling there; a few of the nearby bolts are damp as well. He suggested that the white cold-start smoke from the left exhaust and oily right-side plugs may be due to the fact that 95% of my driving is short trips, which means that the motor doesn't have time to come up to temp, which can create more oil vapor etc.. and can overload the AOS, resulting in oil leaking into the right-bank cylinders. As we know, the right-side cylinder bank exhausts out of the left side. Mechanic said this therefore appears to be an intake problem, not a cylinder problem. He suggested I run the car longer and harder (5,6 even a little 7K RPM) at least once every week or two which may clear up the problem. I will keep y'all and him posted. Note: this mechanic was not crazy about the idea of me taking video of the smoke-machine test (sorry Schnell), and generally has his reservations about these forums. Note #2: Mechanic (who also happens to be a 996 owner) recommended the PCA-sponsored Autocrosses such as the one on 11/13 at nearby El Toro airfield. I think I'll sign up; for the health of my engine of course Anyone want to join? Here's the link: http://www.where2race.com/autocross-...nty-great-park

Excellent news. The autocross should be fun :-). Ask here what pre-fun checks/mods should be done on your car ?

You got your orders. Drive it! Lol.

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this isn't all that uncommon and I don't blame him. everyone is an expert on the internet.

AWDGuy, I am pretty new to these forums (though have been reading daily ever since I got my 996 5-6 months ago). I have no plan to stop my reading and posting, but I can now see the pitfalls. If it weren't for the sage advice of a few smart dudes on this thread, my motor would likely now be out of the car and in the hands of an incompetent mechanic. I wish I could buy everyone here a round.

I hear ya, I owe ashai, jake and Charles a few rounds myself.

So I was explaining all of this to the original shop, and they wondered why I'm having this problem with this 996 and not during my 10 years with my previous car (99 Boxster) which I drove the same way. That got me to thinking about the Fabspeed cold air intake which I have on this car and whether that could be contributing to this problem. I asked the new mechanic and he said yes it might improve this smoke problem. Any agreement or disagreement on this? If no one disagrees, I think I'll shop for a stock airbox.

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I live down the road. I've been meaning to head there at some point

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I can't comment as to whether that intake would contribute to your smoke problem - but that particular intake does get a lot of bad reviews on this forum. Either OEM or the K&N with the heat shield and snorkel seems to be the only rennlist approved intakes.

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Well, the Boxster doesn't use a forged piston that's the same as the 996. I have never seen a Boster engine lose a cylinder. Not once, not ever. This is revealing to that of the root of the 996 cylinder issues. I haven't found an aftermarket intake that works worth a damn yet. They all have more compromise than benefit.

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Thanks, I trust Stuttgart more than I trust Fabspeed etc.., A previous owner put this intake on the car, I prefer stock. Any opinion as to whether the cold air intake could be contributing to this problem?

The only way an intake could make this occur is if the MAF sensor is placed outside the air inlet path enough to reduce the sensor reading. If this happens fuel trim can be added, making for a rich engine, and that causes smoke and oil consumption. Check short and long term fuel trim with the engine at 180F coolant temp, and 200F oil temp, at idle, with the AC off. Report the readings.

He mention aftermarket CAI. I wonder if part of the intake after the MAf is slightly disconnected ?It isvery difficult to visually check this -hence my enthusiasm for the smoke test.

No, I question is the MAF sensor is located in the primary air stream of the intake. Most of these are not, and it leads to issues.

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The plot thickens! Thanks for your input; I will look into this tomorrow and report back.

FYI here's a shot of my engine bay so you can see the intake. Not positive it's Fabspeed as I don't have records of that from the previous owner and there are so many lookalikes. Not sure if this is helpful in answering the MAF sensor question, and I'm planning to discuss with the mechanic tomorrow.

That's a stock airbox with the "orange cap" mod... basically stock, sans the airbox resonator chamber...

(and thus the MAF is where it should be re: the airstream from the airbox) If you decide to get rid of the aftermarket parts, I know a guy who might buy the CF cap.

Fabspeed indeed calls that a "Cold Air Upgrade Kit" for the low low price of $245 (plus shipping). http://www.fabspeed.com/996-carrera-...r-upgrade-kit/ A cold air intake would look like this:

Mr. Miller, Thanks for posting this glorious photo. Hopefully it is also effective.

Thanks everyone. I relayed all your comments about the MAF etc..; mechanic still suggested I replace it with the stock airbox intake boot (part # 99611022157) as it's cheap and may improve the problem. I'm ordering one today and will keep you posted. Schnell, the existing "upgrade kit" intake is in great condition and I'm happy to sell it; email me at bbens at hotmail for more details.

Update 5.5 months later: finally brought the car to Cape Auto in Orange County CA (generally well-regarded here) for an oil change and to help diagnose the frequent but brief left-exhaust cold-start white smoke. They first said that these flat 6 engines by their nature often smoke a bit on cold start, as many have said. After service and road test/inspection, Cape said the car appears to be in excellent shape, runs well with everything within spec. They found no particles on the cut-open oil filter nor on the magnetic drain plug, RKAT measured 0.6 (perfect .00) VRA measured 1.03 (perfect 1.0). Car still burns a quart of oil every 2-3K miles (within spec I understand), otherwise no issues. The PPI/compression test/leakdown tests 5K miles ago all had excellent results. I spent a bit more on this car to find a good one ($27K 5/2016 on this well-optioned C4 Cab with 40K miles and excellent service records) and this is the only real flaw I've been able to find. Of course bore scoring is still a possibility, but absent other symptoms both I and the tech at Cape Auto wonder if it's worth pursuing. This is the 3rd shop who has looked at it and I'm now of the mind to stop worrying and enjoy this beast. Thoughts?

yes a quart of oil every 2/3 k is within spec.................for now .....but if you are driving it normal it is too much and it will only get worse ,i bet the first owner beat it up some how

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Sorry if you mentioned this in the thread but have you had it boroscoped?

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Imho - drive it,enjoy it, keep the preventative maintenance up to your current high standard with an Indie you have evidence is trustworthy and competent. Use the correct oil for a slightly worn engine and do replace oil+filter frequently. Ask your Indie about the spin-on filter upgrade? UOA every 10,000 miles to track any deterioration. Not expensive and useful data.Watch for differences developing between Bank 1&2 in the leakdown tests you do over time.

If the MAF is indeed at fault/in question as Jake mentioned maybe its the removal of the resonator box as this makes mention that it does more than just reduce intake noise: This is also why i've been sceptical regarding the orange cap mod/removing the Helmholtz resonator. Also as DT has mentioned OP has the fabspeed "CAI" the other image with the two pods is their "competition" intake. I'm not a fan of either for various reasons.

Several months ago I removed the Fabspeed cold air "upgrade" (The cheap one which I believe does not affect the stock MAF) and returned it to stock. Unfortunately it had no effect on this cold start smoking issue...

When you drive your car, do you drive it very aggressively?

And did you get to driving it really, and drive it long, like take it out for a weekend and drive 500 miles one way, and 500 back the next day, preferably on a "long and winding road" (and yes, you can sing along!!!!). It sounds (given the mileage sofar) that your car never got the chance to really warm up. Volkert

How often do you change your oil - mileage and also time duration?