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If anyone in the S. Calif area (O.C. preferably) wants to experience the stumble first hand, shoot me a pm. Once you've felt it you'll understand why so many of us are desperately searching for a solution.
Or if anyone knows of some great indy shops down there? I know there's a lot in SoCal. I wish some great shop and mechanic would take up this riddle. It would be a challenge and he'd be a hero.
I have a 2011 997.2 base carrera with 6sp manual. It has a slight stumble at around 2700 rpm. It seems slightly worse in sport mode. I've had car since new and started when had about 10,000 mi. Currently has 34,000 mi. Mine is a very brief stumble that is subtle and always at same rpm so I'm able to drive around it. I've read previous posts about it and assumed it was probably vario cam but not sure. You stated they put a data logger on and concluded you were taking foot off the gas. Could it be an electronic gas pedal issue? I believe my car (997.2) was first to utilize this right? And that would explain the disparity between their logger and your claim.
You stated they put a data logger on and concluded you were taking foot off the gas. Could it be an electronic gas pedal issue? I believe my car (997.2) was first to utilize this right? And that would explain the disparity between their logger and your claim.
My PCNA field tech mentioned the gas pedal position as well - and I could see it in the data chart he showed of all the various systems moving around. There was a vertical line drawn when "the stumble" was felt. Right at that moment, the throttle position did indeed look like it changed, but our theory was the stumble itself causes a shift in the position of the driver (albeit very small). That slight shift could cause a gas pedal movement, but it's another symptom, and not the cause.
As previously mentioned, the throttle position sensor was changed for a stumbler and it made absolutely no difference.
In addition, this stumbling also happens if you use the cruise control function to resume a preset speed. So it seems to have nothing to do with the pedal.
It is difficult to comprehend or appreciate how much time and effort has gone into finding a solution to this problem that appeared out of left field.
And why would anyone trade and buy another 991, only for this feature to possibly appear again??
Picture of the drive recorder...
OMG that's HARDCORE! I doubt any of us chickens are going to hold the magic solution to this ... I fear it needs someone who can read the
telemetry and spot whats in error...
I like the suggestion that its some other component (fuel pump) that is
out of whack and the DME learns to correct for that and introduces the
stumble as a "side-effect" ...
I think the fact reflashing has no effect, and driving in different styles during
relearning also has no effect either, that this would indicate that the cause
is not with the ECU itself but another component that the ECU is compensating for resulting in the side-effect ...
My PCNA field tech mentioned the gas pedal position as well - and I could see it in the data chart he showed of all the various systems moving around. There was a vertical line drawn when "the stumble" was felt. Right at that moment, the throttle position did indeed look like it changed, but our theory was the stumble itself causes a shift in the position of the driver (albeit very small). That slight shift could cause a gas pedal movement, but it's another symptom, and not the cause.
Do you have multiple stumbles within the rpm range you mention or a single one? Mine is a repeatable single hiccup at almost exactly 2700 rpm. Feels like my 82 911SC did when plug wires went bad but instead of multiple misfires it's like a single one at exactly 2700 rpm.
The PIWIS needs to be connected to the car's DME and taken for an extensive test drive with the technician in the car until the problem manifests. Throughout the drive cycle live data monitors need to be observed. The scan tool is capable of live recording. After the symptom occurred you stop the recording and rewind the data to study it from the moment the fault has occurred. My total guess at this point is that I would pay very close attention to fuel pressure at the moment the fault is occurring. I would look at the in tank fuel pump pressure and at the high pressure fuel pump. I believe the PIWIS is capable of displaying those pressures separately. If not,a mechanical fuel pressure gauge needs to be installed,but I doubt that's necessary on a 2013-14 model.
I would also take a very close look at the upstream oxygen sensors on both banks. In closed loop during part throttle they should go rich observing the extra fuel. If they go lean,it might indicate there's a fuel pressure problem,but for a brief moment and not enough to set a check engine light.
One thing to note : if the condition is occurring briefly and can't be associated with a malfunctioning part,there's a possibility it can be corrected through a software update,by changing parameters in the fuel map.
I think your intuition could be right here ... I think there must be some other component that is "out of whack" which is causing the DME to learn a
corrective behavior that results in this unwanted side effect
Anyone have the part number for the upstream O2 sensor? I'm willing to try anything seeing that Porsche has abandoned us.
Swapping parts is not the solution duxsi. Don't do that. This needs to be analyzed and graphed on a scope. A scope is a very very very fast multimeter. If something weird is happening during the drive cycle when the stumble occurs,it might show up on a scope.
This needs patience and many hours of analysis.
I saw the fancy data recorder Porsche installed but I'm not impressed. I don't even know the data they're pulling out of it.
I want to see the fuel trims,I want to see what the O2s are doing,I want to see the MAF values etc. Actually these engines might not be working with a MAF sensor,but with a MAP(Manifold absolute pressure).
Still no resolve. Whoever figures this out will be a hero for all those involved. There was a big list complied somewhere with those affected. Lots of data.
Swapping parts is not the solution duxsi. Don't do that. This needs to be analyzed and graphed on a scope. A scope is a very very very fast multimeter. If something weird is happening during the drive cycle when the stumble occurs,it might show up on a scope.
This needs patience and many hours of analysis.
I saw the fancy data recorder Porsche installed but I'm not impressed. I don't even know the data they're pulling out of it.
I want to see the fuel trims,I want to see what the O2s are doing,I want to see the MAF values etc. Actually these engines might not be working with a MAF sensor,but with a MAP(Manifold absolute pressure).
I hear you loud and clear, and you are correct regarding the MAF-less engines.
How much money is one supposed to pour into this endeavor, based on the fact that this company will not lift a finger other than deny deny deny?
It amazes me that this company can refuse any accountability with ZERO consequences or ramifications.
I hear you loud and clear, and you are correct regarding the MAF-less engines. How much money is one supposed to pour into this endeavor, based on the fact that this company will not lift a finger other than deny deny deny? It amazes me that this company can refuse any accountability with ZERO consequences or ramifications.
I hear you as well and I'm sorry that this is happening to you guys.
Modern DMEs have evolved a lot and can figure out what's happening very accurately,but technicians are relying too much on the computer to signal that there's a problem. Unfortunately a technician despises warranty work because of the way the flat rate system is set up within the company. So,if Porsche tells them to do the initial assessment/read fault and pending codes and send them to the mothership,that's all they'll do. But this is obviously a very intermittent problem that does not set any faults,so they call it " normal ". They will not take the time to investigate further because the mothership will not pay for their time. It's ridiculous I know!
I've just started reading the thread on 6speed. I was not aware of the many people affected by this. I am sure one of you know a good Porsche technician that is willing to investigate this further after hours. Just pay him for his time. He will not be pressed by time like he is when he's at work and can borrow the scan tool. That's what I would do. I wouldn't even bother trying to figure it out through the normal dealership/PCNA channels.
Do you have multiple stumbles within the rpm range you mention or a single one? Mine is a repeatable single hiccup at almost exactly 2700 rpm. Feels like my 82 911SC did when plug wires went bad but instead of multiple misfires it's like a single one at exactly 2700 rpm.
I have multiple stumbles and then a larger stumble at 2700 -ish (but can be up to 3000). The larger stumble seems to be the VarioCam Plus transition. There are different stumbles going on here. Many people report the VarioCam stumble but not the others.
if Porsche tells them to do the initial assessment/read fault and pending codes and send them to the mothership,that's all they'll do. But this is obviously a very intermittent problem that does not set any faults,so they call it " normal ". They will not take the time to investigate further because the mothership will not pay for their time. It's ridiculous I know!
This is exactly why it's so frustrating for us.
1) We're under warranty so we're "supposed" to take it to the dealer.
2) Dealer doesn't see any fault codes and declares it normal.
3) We get mad at the dealer, but really it's a PCNA problem because the dealer won't be compensated for exploratory work without codes.
12-03-2015, 06:50 PM
