flyjets

Morning

I was looking into IMS failures for a friend and ran across this video.
Probably should be mentioned in the Turbo section since they claim its from a 997.1 TT motor.

Never have heard of this issue but I know the Turbo cars are noisy at idle.

One last question why is it some smoke heavily on start and some just puff?
Regardless of sit time.

Ian

Macster

The Mezger engine is noisy at idle -- as frankly so is my 02 Boxster's 2.7l engine -- primarily because there is a lot of hardware in the engine moving about.

In the case of the Turbo engine with its VarioCam Plus system the low lift feature is selected and coupled with the richer fueling at cold idle the engine has a bit of a ragged/rough sound to it. On a still day with the door open I can hear backfires in the exhaust from this rich running.

Low lift is selected to reduce friction and pumping losses at idle to reduce emissions. The engine is fed a rich mixture of fuel because it is cold but also to provide excess fuel for burning in the converters to speed their warm up so the DME can switch to closed loop operation as soon as possible.

The loose bolts failure of the layshaft gear is such a rarity that is frankly not worth worrying about or considering. While I do not think about this failure I always when starting the engine note its sound and if I ever hear a change for the worse in its sound at startup then I might think about the gear bolts loosening although there are other possible and more likely explanations that do not portend engine doom but I'm not going to worry about it at other times.

I have enough on my mind wondering when my 02 Boxster's IMSB will fail especially now when the engine has 275K miles on it and the bearing should have failed already 5 or 6 times...

Oh, as for the difference in smoking there are many factors involved. How fresh the oil is, its type, how much oil is in the engine (or dry sump system), how the car was driven before it was shut off, how hot it got, whether the owner let the engine idle some before shutting off the engine, and so on.

It is my opinion -- theory -- the majority of the smoking arises from the inability of the AOS to remove sufficient oil vapor from crankcase fumes before they are routed to the intake and the engine to be burned.

Under some circumstances this oil vapor is routed to the intake where it impacts the intake wall and collects as oil droplets. If the engine continues to run these are pulled into the engine proper and burned and the exhaust doesn't even show any signs of any smoke.

But if the engine is shut off these oil droplets run down and collect on top of closed intake valves or run into the combustion chamber if the valves are open. Regardless, the oil is burned but incompletely in the engine at the next cold start and oil smoke is the result.

The techs tell me they see this a lot with new cars and used cars on the lot. These engines get started and run for sometimes just seconds and this means these engines smoke upon startup. (My 02 Boxster smoked heavily upon its first start when I was shopping a new Porsche but has not been a prolific cold start smoker.)

If the smoking is short lived, not accompanied by any other engine symptoms, the check CEL remains dark, the techs pay the smoking no mind. And under similar circumstances you should do likewise.

flyjets

Thanks for the explanation. I had been shopping Turbos over the past month and they all puffed smoke but some really had a smoke signature. The one I bought just has a minor puff similar to my beloved Cayman S.

I do hear what sounds like a loose Catalytic Converter heat shield at idle but goes away at 1500 RPM.
Dealer is going to look at it on the 26th any thoughts?

Ian

phillipj

Mine has that rattle from a shield intermittently on start up. I don.t worry about it.. It has done it for years.

Mine will smoke on start up if I had been driving the car hard and then shutting it off without letting the turbos cool...

Smoking on start up is totally normal for P cars..

TT-911

FYI talked about before here, maybe of some use to you :
https://rennlist.com/forums/997-turb...every-day.html

Macster

My only thoughts are that those Turbos you looked at for a while probably led a life very similar to new or used Turbos on the dealer lot and in the showroom.

While smoking at start up is probably not a sign of anything amiss one still when looking at a "new" car pay attention to how the engine sounds, runs.

Then on the road during the test ride then drive pay attention for any signs of exhaust smoke when taking off from a stop and upon hard acceleration after letting the engine slow the car down on closed throttle coast down.

Last be sure you keep the appointment with the dealer. Almost always the noise is from heat shields or some other rather benign source. Be sure you can reproduce the noise on demand when at the dealer.

jayi836

Old thread but very usefully video.