I have a 2005 manual 997 S that has had it's fair share of problems. Under warranty I have had a replacement gearbox due to poor gearshift quality (15K km) and a new engine (18K km) due to probable counter-shaft bearing failure causing engine oil loss, a horrible sound, and cessation of function. Engine was returned to Porsche Germany, but the results of their investigations not known to me or the dealer as far as I know. The car had never been tracked or used inappropriately.

The remaining problem, or issue, I am interested to know if anyone else is putting up with is a brief vibration that sounds like engine "pinking" or pre-detonation that occurs at 2400 rpm under light to moderate load. This has occurred with both the old and the new engines. When the transmission was replaced the clutch and flywheel were also replaced. Dealer assures me that 911 has anti-knock sensors that would not permit pre-detonation.

The vibration definitely comes from the rear of the car is transient (less than a second), but noticeable, and not always easily reproducible, however always at 2400 rpm. Often occurs with gear-change as clutch let out going from 2nd to 3rd gear, but can also occur if gently accelerating from 2400 rpm in 6th gear (which happens to be 100kph) and so am often at that engine speed. It is more associated with light to moderate engine loads, not a heavy foot.

It is annoying and sounds bad, but can't work out what it is. Various 98 octane fuels make no difference. Thanks for input.

 

I have a base model(not S)that has always made the same noise. I cannot really hear it unless the windows are open. I figured that the knock sensor allows this to happen at low rpms. If someone thinks that this is a real problem, please let me know.

 

might be the fuel causing the knocking which you can't really do much about... try running a higher octane fuel than the norm.

i know of a local guy with a 997 who's got some knocking issues but not realy an issue just a noise at this point

 

At certain times I get the characteristic knocking from insufficient octane. To test my theory I put a can of Octane 104 in the tank and never experienced it again (with that tank). Unfortunately, our octane is just not up to the levels required by the motor,--even with knock sensors.

 

Thank you. It seems that there may be some anecdotal evidence of a fuel / octane related issue with the 997 engine. This being my first Porsche it is hard to know what is normal. There is some 100 octane available in Australia so I will try it, but the dealer is going to take the car for a few days shortly and try and isolate the problem because I don't think that it should be happening. The sound (rattley metallic) was evident with both engines, I am sort of hoping it is something else or it is a truly systemic issue in the 997S engine. Will advise.

 

Yes, I have precisely the same engine knock at 2500 rpm or so. I never noticed it before my head gasket replacement at 7K miles. But now, I can reproduce it almost at will. My dealer said that they did not detect excessive knocking when they looked at it. I have found I get less knocking when I use Shell 92 octane, and significantly more frequent and louder knocking when I use Chevron or 76 92 octane.

I find it hard to believe that we can so easily produce knocking under such light load.