View Poll Results: Does your 911 stumble / hesitate
Voters: 98. You may not vote on this poll
Engine Stumble Poll
#76
09-26-2014, 06:55 PM
Probably the easiest way to identify it is to find a long hill and hold the rpm slightly below ~2500 in 3rd or 4th gear. If you have the stumble, slowly increasing through ~2500 rpm will result in a slight but unmistakable feeling that the engine momentarily bogs down, or a very slight misfire. Under light throttle, I can tell whenever I accelerate through the 2500 range without looking at the tach.
Last edited by runner1021; 09-26-2014 at 06:56 PM. Reason: sp.
#77
09-26-2014, 07:12 PM
This is the reason I am so frustrated. Lemon law would be simple if we had a problem that was easily identified or there was a CEL. The problem, I fear, is that you waste your life taking the car into the dealership over and over again. Then you raise a lemon law suit, and you lose due to lack of evidence. Porsche will claim normal operation. I guess you could overcome some of this if you have a good service writer that believes you and is on your side. The language they put in your service records would be rather important.
I feel so stuck. My options are:
1.) I can't sell the car private party. Even if I were immoral enough to try and dupe someone into buying my flawed car, they would eventually come back to burn my house down after they realized I scammed them.
2.) I can trade the car to a dealer, but I'm going to get smoked. There is no way I'm going to roll the dice on another C2S, so it's a GT3 or Turbo. I don't want to own any other car. I figure the GT3 has a completely different engine, so the chance of having a similar problem is mitigated. It will be hard to get, but I learned today it can be done.
3.) I just live with it and resent my formerly perfect car.
I've been shopping GT3s today, so I may be taking the $20-$30K loss and moving on. Let's hope I don't jump out of the frying pan into the fire. The other problem is that I beat the daylights out of my wife the past few years with cars. She understands this one isn't my fault, but it's hard to broach the topic of losing $25K and spending a net $50,000 more right after buying an $80,000 M3. Sigh...
I feel so stuck. My options are:
1.) I can't sell the car private party. Even if I were immoral enough to try and dupe someone into buying my flawed car, they would eventually come back to burn my house down after they realized I scammed them.
2.) I can trade the car to a dealer, but I'm going to get smoked. There is no way I'm going to roll the dice on another C2S, so it's a GT3 or Turbo. I don't want to own any other car. I figure the GT3 has a completely different engine, so the chance of having a similar problem is mitigated. It will be hard to get, but I learned today it can be done.
3.) I just live with it and resent my formerly perfect car.
I've been shopping GT3s today, so I may be taking the $20-$30K loss and moving on. Let's hope I don't jump out of the frying pan into the fire. The other problem is that I beat the daylights out of my wife the past few years with cars. She understands this one isn't my fault, but it's hard to broach the topic of losing $25K and spending a net $50,000 more right after buying an $80,000 M3. Sigh...
ChuckJ
#78
09-26-2014, 07:40 PM
I still contend that the dealers have been put on notice by PCNA to claim that any stumbles or hesitations are to be considered normal.
I've only found one instance where the stumble was addressed and fixed (on a 996):
http://rennlist.com/forums/996-forum...999-996-a.html
(see post #5)
#79
09-26-2014, 07:56 PM
Believe me, the dealers are coached to just recite the script as it comes from the top down. You don't follow the script, you don't get paid for any work and get penalized. The dealers obviously do whatever the string holders direct.
"A little hesitation" no problem.
"A little GT3 fire" big problem.
#80
09-26-2014, 08:05 PM
And therein lies the problem. The dealer will write it up as "customer complains of engine hesitation during light acceleration." And then he'll turn around and write "test drove car and found acceleration to be normal." (They all do that)
I still contend that the dealers have been put on notice by PCNA to claim that any stumbles or hesitations are to be considered normal.
I've only found one instance where the stumble was addressed and fixed (on a 996):
http://rennlist.com/forums/996-forum...999-996-a.html
(see post #5)
I still contend that the dealers have been put on notice by PCNA to claim that any stumbles or hesitations are to be considered normal.
I've only found one instance where the stumble was addressed and fixed (on a 996):
http://rennlist.com/forums/996-forum...999-996-a.html
(see post #5)
ChuckJ
#81
09-26-2014, 09:20 PM
Registered User
Join Date: Jun 2004
Location: New Jersey(outside Phila)
Age: 63
Posts: 2,597
Rep Power: 125 
Probably the easiest way to identify it is to find a long hill and hold the rpm slightly below ~2500 in 3rd or 4th gear. If you have the stumble, slowly increasing through ~2500 rpm will result in a slight but unmistakable feeling that the engine momentarily bogs down, or a very slight misfire. Under light throttle, I can tell whenever I accelerate through the 2500 range without looking at the tach.
#82
09-27-2014, 10:43 AM
Here's a few thing I found:
1. Today I received a call that my problem is fixed and my car is ready. According to the service manager, it's a problem with the "crankshaft position indicator" which may need to be shimmed in order to make proper contact. It's not a common problem - there's no service update (or whatever they call it) published, but it's not the first that Porsche higher-ups had heard of it. In other words, Porsche was aware of a problem but hasn't passed on the info to their dealers. Nice
2. Since I started turning off PSM the car takes off much better.
I wont drive with PSM on anymore.
Also, I found that you should use lower throttle input initially and then wait untill the clutch fully engages, before applying heavy throttle.
But do it before the car upshifts to 2nd or you bog and then get another delay, before it drops back to 1st. (A possible test to narrow down issues...?)
3. I've been told by a friend in Stuttgart who is a VP of Engineering with MBZ who has friends that are engineers at Porsche that almost every driveability issue that comes up these days are software/engine management update related. Not mechanical.
He also told me with some dismay that there are terrible losses in communication with service managers at dealerships. Mostly the frustration is on the German side with US dealership service techs not being educated or have enough experience with their own products. Maddening for owners who have driveability issues like this that should be simple to correct but that the procedure gets mis managed on our end.
4. Porsche 2012 991S PDK: acceleration hesitation - YouTube
5. Here is a thought related to that- does your PSE button actually work? The vacuum valve that controls the exhaust has been known to fail. From what I know of the PSE, when it is on the valves are open at idle, closed until 3-4k and then open again. If the valves failed, they would be open the whole time, which at that low rpm would reduce torque maybe just enough to throw off the PDK, just like what is happening with the aftermarket xpipe
6. Replacing both pre-cat lambdas the issue.
As an aside, I'm rapidly starting to learn that these cars don't throw fault codes until something very major is wrong. Sensors (especially MAF/Lambdas) can be far enough away from spec to have the car running like a dog, but without throwing a code. Cursory use of the PIWIS just to look for fault codes will not find the majority of issues that can cause the cars to run less then optimally. The PIWIS is capable of reading every conceivable operating parameter in real time, but without someone who REALLY understands engines (mechanically) and the DME (in real depth) to interpret what they're seeing, most faults will never be found"
1. Today I received a call that my problem is fixed and my car is ready. According to the service manager, it's a problem with the "crankshaft position indicator" which may need to be shimmed in order to make proper contact. It's not a common problem - there's no service update (or whatever they call it) published, but it's not the first that Porsche higher-ups had heard of it. In other words, Porsche was aware of a problem but hasn't passed on the info to their dealers. Nice
2. Since I started turning off PSM the car takes off much better.
I wont drive with PSM on anymore.
Also, I found that you should use lower throttle input initially and then wait untill the clutch fully engages, before applying heavy throttle.
But do it before the car upshifts to 2nd or you bog and then get another delay, before it drops back to 1st. (A possible test to narrow down issues...?)
3. I've been told by a friend in Stuttgart who is a VP of Engineering with MBZ who has friends that are engineers at Porsche that almost every driveability issue that comes up these days are software/engine management update related. Not mechanical.
He also told me with some dismay that there are terrible losses in communication with service managers at dealerships. Mostly the frustration is on the German side with US dealership service techs not being educated or have enough experience with their own products. Maddening for owners who have driveability issues like this that should be simple to correct but that the procedure gets mis managed on our end.
4. Porsche 2012 991S PDK: acceleration hesitation - YouTube
5. Here is a thought related to that- does your PSE button actually work? The vacuum valve that controls the exhaust has been known to fail. From what I know of the PSE, when it is on the valves are open at idle, closed until 3-4k and then open again. If the valves failed, they would be open the whole time, which at that low rpm would reduce torque maybe just enough to throw off the PDK, just like what is happening with the aftermarket xpipe
6. Replacing both pre-cat lambdas the issue.
As an aside, I'm rapidly starting to learn that these cars don't throw fault codes until something very major is wrong. Sensors (especially MAF/Lambdas) can be far enough away from spec to have the car running like a dog, but without throwing a code. Cursory use of the PIWIS just to look for fault codes will not find the majority of issues that can cause the cars to run less then optimally. The PIWIS is capable of reading every conceivable operating parameter in real time, but without someone who REALLY understands engines (mechanically) and the DME (in real depth) to interpret what they're seeing, most faults will never be found"
I couldn't tell if when you stomped on it the tach immediately went to 3500, did it or did the clutch lock up quickly at 1000 or 1500?
ChuckJ
#84
09-27-2014, 11:01 AM
Join Date: Jul 2012
Location: Just visiting the planet
Posts: 1,055
Rep Power: 86 
I've been shopping GT3s today, so I may be taking the $20-$30K loss and moving on. Let's hope I don't jump out of the frying pan into the fire. The other problem is that I beat the daylights out of my wife the past few years with cars. She understands this one isn't my fault, but it's hard to broach the topic of losing $25K and spending a net $50,000 more right after buying an $80,000 M3. Sigh...
Despondency and frustration is exactly what they're banking on and in numbers we do have a leg to stand on.
I when it comes to LL arbitration I will find another owner within the 70% (with the exact same car) as my benchmark. Either make his car stumble or get rid of my stumble. "Normal" is ~ 100% not 30%.
I know something simple has ceased to operate in our cars and the DME isn't picking it up for reasons discussed earlier.
Problems / changes don't just appear without a cause resulting in an effect.
Another $50K of your hard earned money to this company for a problem that you did nothing to create? Hell no...
#85
09-27-2014, 07:21 PM
Registered User
Join Date: Jun 2004
Location: New Jersey(outside Phila)
Age: 63
Posts: 2,597
Rep Power: 125
I checked today multiple times and in 3rd and 4th under light and medium throttle conditions on level ground and up hill. I don't feel any stutter.
#86
09-27-2014, 07:23 PM
I just finished reading an article about direct injection in the current edition of Excellance. Has anyone considered the possibility that the problem may be related to a high pressure fuel pump malfunction and failure as the symptoms described here sound like fuel starvation to me. This may explain why not all 991 have this issue as there may have been a bad run of pumps. Further it may explain why it's hard to detect as no faults may be recorded as pumps have various pressures when operating by design
Last edited by rnl; 09-27-2014 at 07:36 PM.
#87
09-28-2014, 11:22 AM
Just out of curiosity, how many owners with the stumble have also encountered the no-start (engine won't restart when warm after having been shut down for a short period) and/or engine stalling symptoms? (After a year since my previous problems with the no-start, I all of a sudden had it reappear recently, along with engine stalling below approx. 1000 rpm. Planned on taking it in, but of course the problem magically disappeared the next day). Surprisingly, the supposed fix for this has been to shim the camshaft position sensor. Interestingly, this sensor also apparently comes into play in the VarioCam plus system:
"A modified rotor is fitted to the intake camshafts of both cylinder banks. Due to the rotor position, the Hall sensor determines the current position of the intake camshaft 4 times per camshaft revolution and relays this value to the control unit. This determines precisely the position of both intake camshafts."
I surely can't solve the problem, but I sincerely wish someone at Porsche would get off their duff and get to the bottom of this.
"A modified rotor is fitted to the intake camshafts of both cylinder banks. Due to the rotor position, the Hall sensor determines the current position of the intake camshaft 4 times per camshaft revolution and relays this value to the control unit. This determines precisely the position of both intake camshafts."
I surely can't solve the problem, but I sincerely wish someone at Porsche would get off their duff and get to the bottom of this.
#88
09-28-2014, 11:25 AM
I just finished reading an article about direct injection in the current edition of Excellance. Has anyone considered the possibility that the problem may be related to a high pressure fuel pump malfunction and failure as the symptoms described here sound like fuel starvation to me. This may explain why not all 991 have this issue as there may have been a bad run of pumps. Further it may explain why it's hard to detect as no faults may be recorded as pumps have various pressures when operating by design
#90
09-29-2014, 06:07 PM
To be honest I'm surprised by the 1/3 population right now. Makes me feel a little better knowing I'm not alone. I know many of us are actively working to find a solution to this. With the more people becoming aware of this hopefully one of us will have a break through.