991.1 GT3 Revving Issue
 

My 2014 GT3 has developed an issue. After a short period of hard driving, it no longer freely revs, particularly past 7.5k.

I've attached 2 videos. One shows the normal revving of the engine under full load and you can clearly hear the normal, distinctive metallic sound between 8-9k RPM. The other shorter video shows it being much more laboured, revving more slowly and no metallic sound that we all love. Car feels considerably slower when it is in this mode.

No engine lights, no other issues to note on the car. Anyone have any ideas? The dealer is unable to find a fault so I've been out to take videos for them but didn't know if anyone had seen this before... I know the sound is generated from the induction path of the engine so thought it could be related to that somehow...

Normal Engine Reving -
Engine Problem -

Think you might have to make a longer vid of the engine issues.

I don't see an issue, I think your being paranoid. These vehicles have multiple sensors which would pickup issues. Drive it and enjoy it until the engine blows and get a new one.
You won't get anywhere without getting some fault codes. Make sure your oil/filters/spark plugs are done too.

There is certainly an issue. On my latest trackday the difference in speed down the straight before and after the issue becoming present was between 15-18 Mph. It is very evident in the car.

Not to worry if you can't see/hear - probably need to put up a longer video.

If possible, please post a longer video of the problem...

15-18 mph? what was your top speed before and after on track? I'm not a tech but I would think anything going on that would create that much difference would throw a code. Some basic stuff that came to my mind: air filters clogged, bad gas. You didn't by chance get a tank full of regular? Stations have been known to get regular/premium switched in their storage tanks.

So it was 158mph on lap 2 and from lap 4 onwards, never above 142mph. Just seems odd to me that it only occurs once it's had say 10 minutes of hard driving. Almost like something doesn't work when it gets hot but oil temp never going over 102 degrees. Unfortunately on the fuel side, this has been going on for quite a few tanks now - had initially been my thoughts.

I've put a longer video below. During all acceleration, throttle is fully depressed. Note the first time through the gears, the revs climb very slowly up until about 8700 and then you suddenly hear the metallic sound kick in (typically this happens around 7800 as you know) and it race to the redline. On the second pull at the end of the video, you simply see the revs climb very slowly - no normal metallic noise. It's already behaving incorrectly the first pull but the second I guess it's that little bit hotter so the whole range revs at the slower pace.

Your most recent video doesn't really illustrate the problem you say you're having. On the first half of the video you do a run up from 2nd through 3rd and into 4th. On the 2nd half of the video you only run from 2nd into 3rd.

In the 1st half of the video, based on my stopwatch, it takes you about 2.5 to 2.6 seconds to get from 6000 RPM in 2nd gear to your next gear change.

In the 2nd half of the video, based on my stopwatch, it also takes you about 2.5 to 2.6 seconds to get from 6000 RPM in 2nd gear to your next gear change. It doesn't appear to be any slower. The metallic audio issue also isn't coming through. I'm not saying you aren't having a problem, but it's not showing up in the videos you posted.

Maybe a sticky butterfly in the throttle body?

That sounds like a really good suggestion - thank you. Will investigate

Thank you for looking. For me, on the first video (good rev) I time 1.8 seconds from 6k to shift up in 2nd. All shifts here are done in auto mode with PDK sport on and throttle fully depressed.

In the most recent posted video I time 2.06 seconds for 6-9k in 2nd gear at the end of that video.

The difference is more and more discernible in say 4th gear when revs are naturally climbing slower than 2nd but even here it is visibly 10% slower at least.

I disagree. The audio is very clear to me. At 8700 it clearly changes note whereas it changed much earlier in the 1st video . I'm wearing some very nice headphones, so that might be why I hear it and you don't.

Glad it's not just me seeing it.... Diagnosing is going to be a nightmare with no fault codes etc but will look at throttle bodies first. Thank you all.

I do see the problem you're talking about in your videos. It took me a second to notice but it's there. Suggestions as already mentioned: sticky butterfly valve in throttle body, dirty/clogged intake filters, bad gas, bad injectors or spark plugs. Those are my best guesses.

Thank you. The issue is, it only comes about after a good 10 minutes of hard driving at least. So replicating for the dealer is quite hard... I assume it has to be heat induced but as mentioned, oil temp never goes that high.

Will be up on the ramps just after Christmas so hope to find out then. Maybe stick butterfly valves when hot is what I'm thinking...