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    • Porsche 991.2 9A2 3.0 Start/Stop contributing to premature shaft/bearing wear?

      The Porsche 991.2 models equipped with the 9A2B6 3.0 twin turbocharged flat-6 engine have a Start/Stop function like many modern cars designed to improve fuel economy. This system can be disabled but those using it should be aware of potential premature wear issues.


      Take a look at this turbine shaft off a 991.2 Carrera with only 4000 miles. Yes, 4000 not 40,000. The turbine shaft shows bearing contact. Definitely more wear than expected on a car with such low mileage.

      The theory is that the loss of oil pressure during a stop lets the shaft move and contact the journal bearing.

      Is this a problem? Perhaps. It depends how long one keeps the car and how it is driven. One way to make sure there will not be a future problem is to switch to ball bearing turbochargers.

      Either way, Porsche is building cars designed to just make it through the warranty period these days like everyone else. It will be interesting to see if there are turbo failures in higher mileage cars.

      Disabling the Start/Stop feature when driving may be prudent for 991.2 owners as well.


      Photo Credit: Mimo Technik

      This article was originally published in forum thread: Porsche 991.2 9A2 3.0 Start/Stop contributing to premature shaft/bearing wear? started by Sticky View original post
      Comments 19 Comments
      1. F16HTON's Avatar
        F16HTON -
        I had always suspected this from day one. Always turn of start/stop as part of my pre-flight check routine.

        Shaft has an abrupt neck down on it, similar to the IS38 turbos on VAG products, harmonic collisions cause those shafts to break daily.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by F16HTON Click here to enlarge
        I had always suspected this from day one. Always turn of start/stop as part of my pre-flight check routine.
        I just put it right and sport and it does it for me.
      1. F16HTON's Avatar
        F16HTON -
        Click here to enlarge Originally Posted by Sticky Click here to enlarge
        I just put it right and sport and it does it for me.
        Sport is my only pre flight check Click here to enlarge. I wait until the RPMs drop after the cats are warmed up.
      1. 3DMetal's Avatar
        3DMetal -
        That is a surprising amount of bearing contact marks on the shaft with such low miles. The turbos spinning down with no oil pressure is what i suspect is happening. The Auto-Stop/Start kills throttle even before you reach your stop ( as your coasting to a light for example. ). I worry other bearings in the engine will also have trailing oil pressure issues but non as easily replaceable as the turbos themselves.

        Maybe a tuner can program and set the default for auto start to "off", or it can be done with a simple ad-in module you connect in-between the harness and center console switch box, or even something on the can bus to flip that state on ign start.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by 3DMetal Click here to enlarge
        I worry other bearings in the engine will also have trailing oil pressure issues but non as easily replaceable as the turbos themselves.
        911 Turbo models don't seem to have any problems?
      1. 3DMetal's Avatar
        3DMetal -
        991 turbo seems to remember the auto/start stop state. ( depends on year and sometime options )
        Comforting to know that they dont have any issues with the turbos longevity *yet. Similar bearings in both , so nothing special or changed. Ball bearing turbos are much much more tolerant to oil pressure loss, as they do not rely on oil to keep the bits apart.


        Update: Found this option. !!! Can be coded in !! or tuners can add the functionality. ( they did that for the Sport mode on the E46 M3 easily )

        Attachment 55377
      1. Stevenh's Avatar
        Stevenh -
        My car never goes into start/stop unless I manually activate it. Can it be saved in the driver settings?
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by Stevenh Click here to enlarge
        My car never goes into start/stop unless I manually activate it. Can it be saved in the driver settings?
        For the 991.2 it always resets but sport mode automatically turns it off.

        Someone has a module I think that has the car remember settings like the Start/Stop being off but I'd have to go find it.
      1. ///M3THOD's Avatar
        ///M3THOD -
        Wow. This is interesting.. and also really not good. Any turbo failures occurring while tuned will certainly be under warranty scrutiny.

        On the positive side, they should be easy to replace relatively cheaply, assuming they don’t grenade and end up in the cylinders.

        I never run my car with start/stop, but now I will be extra precautious.
      1. quattr0's Avatar
        quattr0 -
        A bit surprised w this issue. I guess the '15 and '16 TT/TTS dont have this issue?
      1. F16HTON's Avatar
        F16HTON -
        Click here to enlarge Originally Posted by quattr0 Click here to enlarge
        A bit surprised w this issue. I guess the '15 and '16 TT/TTS dont have this issue?
        15-16 TTS is a E888 engine and the K04 turbo was pretty robust. The Gen III TTS is a MQB and has the IS38.

        The IS38 is more robust than the IS20, however I have seen dozens of failures.

        I have a friend who IS20 A3 which failed on the way home from the dealership brand new.
      1. quattr0's Avatar
        quattr0 -
        Sorry man. I meant to ask 911 Turbo and S as they are also turboed to see this was a known issue.
      1. 3DMetal's Avatar
        3DMetal -
        No trending failures of stock or modded 911 turbo cores. These are robust.
      1. ///M3THOD's Avatar
        ///M3THOD -
        Do we actually know of any failures of .2 turbo's yet?
      1. F16HTON's Avatar
        F16HTON -
        Click here to enlarge Originally Posted by ///M3THOD Click here to enlarge
        Do we actually know of any failures of .2 turbo's yet?
        I have yet to see any, my technician friends have not either.
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by ///M3THOD Click here to enlarge
        Do we actually know of any failures of .2 turbo's yet?
        Nah, way too early. This likely wouldn't rear its head for a few years at least or for people who heavily track.
      1. John Mclane's Avatar
        John Mclane -
        Since 16 the german was "updated" and the car wont remember the ASS off no longer (according to a Porsche technician). Coding Porsches since the.2 model is notoriously difficult. The module Sticky mentioned here, if the same I saw, connects under the ASS button panel and remember your settings.
        The behavior on the Cayenne is quite worse as it shuts down the engine before you come to a stop, such as approaching a curve cross-traffic. Very unsettling as the steering wheel hardens in the middle of a slow curve. Just a matter of time to cause an accident.
        Funny how modern things are. Stopping too much is an issue but apparently flogging it in a race track is not (Disclaimer - the latter will void your warranty).
      1. Sticky's Avatar
        Sticky -
        Click here to enlarge Originally Posted by John Mclane Click here to enlarge
        The module Sticky mentioned here, if the same I saw, connects under the ASS button panel and remember your settings.
        Yep that's the one. I'd prefer a real coding solution but it is what it is.
      1. F16HTON's Avatar
        F16HTON -
        One think I have noticed is that the key will remember you climate control settings, I have minse set to AC on on level one. Each time I use my key for entry and access, when I start the car the HVAC is running which acts as a buffer against auto start/stop.

        With that being said, I still prefer to put the car in sport mode.