Misfires and rpm shudder (plugs, coils and battery replaced)
06-24-2023, 12:06 PM
#16
Rennlist Member
A long time later, but I'm still having troubles with my Cayenne..It's been in and out of the Porsche workshop many times but in the end the result is the same. I'll summarize here what hasn't worked and what I currently suspect to be the cause.
The workshop has ruled out the transfer case both by disconnecting the stepper motor and by trying to provoke it to slip during driving (braking and accelerating at a slow speed simultaneously, which they said causes it to slip if in a bad state).
All fuel injectors have been replaced.
Software (ECU?) has been updated.
Cylinders have been camera inspected and showed nothing the workshop deemed out of the ordinary.
Valves have been inspected and did have "some" carbon buildup (?) on them, but the workshop deemed them unlikely to be the cause.
Now, to the light at the end of the tunnel (I hope): The day after the injectors were replaced and the software updated I got a check engine light within 2min after first start-up. I was driving slow and cautiously and the light went on without any other indication to me that anything had just happened. About 30sec later the light went out again. I took the car to the same Porsche workshop and they said they could see a fault code related to a knock sensor, but that it was now historic and that it was unrelated to the problems/symptoms displayed by my car.
I took the car home without action but it got me thinking about, and reading up on, knock sensors. The way I understand it, a knock sensor could potentially malfunction in such a way that it is "over-sensitive", which would make the ECU think there were engine knocks when there in fact aren't, right?
And if so, I also understand that ECU's of some manufacturers learn the circumstances (load, RPM etc) surrounding these supposed knock events and try to avoid them happening again in the future by (indirectly, by ignition timing and maybe other adjustments) limiting performance, correct?
This would explain why the car feels a lot better after resetting the "ECU learning" (either directly by the workshop or by disconnecting the battery to replace it with a new one) and gradually gets worse, as well as the lack of power I feel my Cayenne has. I don't know if it can explain the shudders though, or if this maybe is the direct result of the ECU momentarily adjusting engine parameters to avoid "learned knock events".
Please poke holes in my suspicion of it being an "over-sensitive" knock sensor if you see any problems with the theory, as my understanding of the knock sensor and its interplay with the ECU may be incorrect and incomplete.
The workshop has ruled out the transfer case both by disconnecting the stepper motor and by trying to provoke it to slip during driving (braking and accelerating at a slow speed simultaneously, which they said causes it to slip if in a bad state).
All fuel injectors have been replaced.
Software (ECU?) has been updated.
Cylinders have been camera inspected and showed nothing the workshop deemed out of the ordinary.
Valves have been inspected and did have "some" carbon buildup (?) on them, but the workshop deemed them unlikely to be the cause.
Now, to the light at the end of the tunnel (I hope): The day after the injectors were replaced and the software updated I got a check engine light within 2min after first start-up. I was driving slow and cautiously and the light went on without any other indication to me that anything had just happened. About 30sec later the light went out again. I took the car to the same Porsche workshop and they said they could see a fault code related to a knock sensor, but that it was now historic and that it was unrelated to the problems/symptoms displayed by my car.
I took the car home without action but it got me thinking about, and reading up on, knock sensors. The way I understand it, a knock sensor could potentially malfunction in such a way that it is "over-sensitive", which would make the ECU think there were engine knocks when there in fact aren't, right?
And if so, I also understand that ECU's of some manufacturers learn the circumstances (load, RPM etc) surrounding these supposed knock events and try to avoid them happening again in the future by (indirectly, by ignition timing and maybe other adjustments) limiting performance, correct?
This would explain why the car feels a lot better after resetting the "ECU learning" (either directly by the workshop or by disconnecting the battery to replace it with a new one) and gradually gets worse, as well as the lack of power I feel my Cayenne has. I don't know if it can explain the shudders though, or if this maybe is the direct result of the ECU momentarily adjusting engine parameters to avoid "learned knock events".
Please poke holes in my suspicion of it being an "over-sensitive" knock sensor if you see any problems with the theory, as my understanding of the knock sensor and its interplay with the ECU may be incorrect and incomplete.
I had been thinking along the lines of a faulty fuel injector, but a faulty knock sensor makes sense. The lack of codes puzzles me, but my code reader is not high end, so maybe my mechanics high end code reader will show something.
I have a few months remaining on my transfer case warranty, so I’ll have them look at that, too. Mike
Last edited by mk85911; 06-24-2023 at 02:01 PM.
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TXCOMT (06-24-2023)
05-27-2024, 09:31 AM
#17
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Exactly the same issue with my 2011 cayenne turbo
A long time later, but I'm still having troubles with my Cayenne..It's been in and out of the Porsche workshop many times but in the end the result is the same. I'll summarize here what hasn't worked and what I currently suspect to be the cause.
The workshop has ruled out the transfer case both by disconnecting the stepper motor and by trying to provoke it to slip during driving (braking and accelerating at a slow speed simultaneously, which they said causes it to slip if in a bad state).
All fuel injectors have been replaced.
Software (ECU?) has been updated.
Cylinders have been camera inspected and showed nothing the workshop deemed out of the ordinary.
Valves have been inspected and did have "some" carbon buildup (?) on them, but the workshop deemed them unlikely to be the cause.
Now, to the light at the end of the tunnel (I hope): The day after the injectors were replaced and the software updated I got a check engine light within 2min after first start-up. I was driving slow and cautiously and the light went on without any other indication to me that anything had just happened. About 30sec later the light went out again. I took the car to the same Porsche workshop and they said they could see a fault code related to a knock sensor, but that it was now historic and that it was unrelated to the problems/symptoms displayed by my car.
I took the car home without action but it got me thinking about, and reading up on, knock sensors. The way I understand it, a knock sensor could potentially malfunction in such a way that it is "over-sensitive", which would make the ECU think there were engine knocks when there in fact aren't, right?
And if so, I also understand that ECU's of some manufacturers learn the circumstances (load, RPM etc) surrounding these supposed knock events and try to avoid them happening again in the future by (indirectly, by ignition timing and maybe other adjustments) limiting performance, correct?
This would explain why the car feels a lot better after resetting the "ECU learning" (either directly by the workshop or by disconnecting the battery to replace it with a new one) and gradually gets worse, as well as the lack of power I feel my Cayenne has. I don't know if it can explain the shudders though, or if this maybe is the direct result of the ECU momentarily adjusting engine parameters to avoid "learned knock events".
Please poke holes in my suspicion of it being an "over-sensitive" knock sensor if you see any problems with the theory, as my understanding of the knock sensor and its interplay with the ECU may be incorrect and incomplete.
The workshop has ruled out the transfer case both by disconnecting the stepper motor and by trying to provoke it to slip during driving (braking and accelerating at a slow speed simultaneously, which they said causes it to slip if in a bad state).
All fuel injectors have been replaced.
Software (ECU?) has been updated.
Cylinders have been camera inspected and showed nothing the workshop deemed out of the ordinary.
Valves have been inspected and did have "some" carbon buildup (?) on them, but the workshop deemed them unlikely to be the cause.
Now, to the light at the end of the tunnel (I hope): The day after the injectors were replaced and the software updated I got a check engine light within 2min after first start-up. I was driving slow and cautiously and the light went on without any other indication to me that anything had just happened. About 30sec later the light went out again. I took the car to the same Porsche workshop and they said they could see a fault code related to a knock sensor, but that it was now historic and that it was unrelated to the problems/symptoms displayed by my car.
I took the car home without action but it got me thinking about, and reading up on, knock sensors. The way I understand it, a knock sensor could potentially malfunction in such a way that it is "over-sensitive", which would make the ECU think there were engine knocks when there in fact aren't, right?
And if so, I also understand that ECU's of some manufacturers learn the circumstances (load, RPM etc) surrounding these supposed knock events and try to avoid them happening again in the future by (indirectly, by ignition timing and maybe other adjustments) limiting performance, correct?
This would explain why the car feels a lot better after resetting the "ECU learning" (either directly by the workshop or by disconnecting the battery to replace it with a new one) and gradually gets worse, as well as the lack of power I feel my Cayenne has. I don't know if it can explain the shudders though, or if this maybe is the direct result of the ECU momentarily adjusting engine parameters to avoid "learned knock events".
Please poke holes in my suspicion of it being an "over-sensitive" knock sensor if you see any problems with the theory, as my understanding of the knock sensor and its interplay with the ECU may be incorrect and incomplete.
As you did, I changed plugs coil packs, crank position sensor, fuel filter, camshaft actuator solenoids, and replaced broken cam cover bolts so no air leaks.
No codes, but recently the car died rolling up to a traffic signal, cranked over and almost started but sounded awful, after 20 minutes rest, the car started and ran perfectly???? ECU breaking down??
I followed up with a system check with icarsoft, this showed up both banks running rich. And ' P1572 Control unit run on not ended correctly' fault.
The downstream lambda sensors showed zero regulation????? Maybe this is the issue?
in the meantime I do have a message bank 2 camshaft invalid signal, so that my next stop as it's a simple fix.
Your experience of resetting ECU via battery disconnecting etc, points to either bad data being sent to the ECU, or ECU issue.
The jumping rev counter and hesitation (even when stationary) point to electrical ignition issues, which would also cause banks to run rich as unburned fuel and air will play havoc with the lambda readings.
Ps also changed the transfer case as my first move, Doh!!!
please let me know if you find the cure.
06-07-2024, 01:33 AM
#18
my 2015 CTT which i bought a few mths ago and have put on 3k of its 54k miles started having the same issue the other day. I also had a error light go on for the PSM along with a check engine light.
I knew the battery was original, so i replaced it. PSM error light went away, but engine check light is still on and its still misfiring. both under idle as well as acceleration.
my indiesscan tool says cylinder 8 is misfiring. Replaced plug and coil, and no improvement.
going to try cleaning the injectors tomorrow, but curious if the knock sensor is the issue.
trying to avoid the dealer as there is no warranty.
I knew the battery was original, so i replaced it. PSM error light went away, but engine check light is still on and its still misfiring. both under idle as well as acceleration.
my indiesscan tool says cylinder 8 is misfiring. Replaced plug and coil, and no improvement.
going to try cleaning the injectors tomorrow, but curious if the knock sensor is the issue.
trying to avoid the dealer as there is no warranty.
06-07-2024, 04:12 AM
#19
2nd Gear
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Next steps??
I did visit the main dealer here in Muscat, the service manager explained to me that 'engines need air, fuel and a spark, we will start replacing the lowest cost items first' 
Anyhow, the readings of '0' for both downstream lambda sensors is sounding alarm bells. When I get the chance, I'll be renewing them/checking wiring.
Anyhow, the readings of '0' for both downstream lambda sensors is sounding alarm bells. When I get the chance, I'll be renewing them/checking wiring.
06-08-2024, 12:58 PM
#20
there is another thread about the PSM and check engine light going on same time. Which is what mine did. The theory is that waiting too long to replace the battery and the plugs (which was the case with the used but new to me CTT) weakens the coils to where they don't realiably work. I replace all the coils and plugs after i replaced the battery and now i have no more misfires, check engine light or PSM error light.
Only been a few days, so will see if issues comes back later.
Only been a few days, so will see if issues comes back later.
Last edited by mallenbiker; 06-09-2024 at 12:17 PM.
06-09-2024, 03:54 AM
#21
Reading this thread is very frustrating. I was an audi tech at a dealer in the bay area for 20 years - this guessing and throwing parts at cars only happened by the junior techs. There are diagnostic steps and tests to isolate automotive problems! It's rare (but sometimes happens) to just replace the least expensive parts first. Find a good independent German car or porsche specialist and have them DIAGNOSE the problem. It could be a weak fuel pump, an intermittent crank sensor signal.... or many many other things! I feel for you and hope you find a smart technician.
06-09-2024, 12:16 PM
#22
Reading this thread is very frustrating. I was an audi tech at a dealer in the bay area for 20 years - this guessing and throwing parts at cars only happened by the junior techs. There are diagnostic steps and tests to isolate automotive problems! It's rare (but sometimes happens) to just replace the least expensive parts first. Find a good independent German car or porsche specialist and have them DIAGNOSE the problem. It could be a weak fuel pump, an intermittent crank sensor signal.... or many many other things! I feel for you and hope you find a smart technician.
It's way more economical to try the easy fixes first than going to a specialty Porsche shop or a dealer.
06-09-2024, 12:57 PM
#23
Diagnostic tools??
No. I meant the tech with years of experience that uses tools. You need a solid knowledgeable technician that understands the car and the systems and doesn't guess. They're out there. In fact, most shops have at least 1 really good guy that's paid very well and the rest of the employee are oil changes / under paid kids.
And I'm sorry but i disagree that it's more economical to spend money on plugs and coils and sensors and not having your car running right for weeks versus paying one time for a diag fee of a few hours to have it fixed right the first time.
No. I meant the tech with years of experience that uses tools. You need a solid knowledgeable technician that understands the car and the systems and doesn't guess. They're out there. In fact, most shops have at least 1 really good guy that's paid very well and the rest of the employee are oil changes / under paid kids.
And I'm sorry but i disagree that it's more economical to spend money on plugs and coils and sensors and not having your car running right for weeks versus paying one time for a diag fee of a few hours to have it fixed right the first time.
Last edited by Hayabusa3; 06-09-2024 at 12:59 PM.
06-17-2024, 07:59 PM
#24
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LPFP/HPFP on 2011 CTT
If any of you guys are still reading this thread, this could be helpful ... My story: A few weeks ago after changing out plugs & coils, I got a (yellow) Check Engine light when passing a car on a significant hill. It was the Low Pressure Fuel Pump (LPFP). We replaced the LPFP at my local Euro auto shop and crossed our fingers that nothing would go wrong with the High Pressure Fuel Pump (HPFP) since it's much more expensive. Up to this point, I'd never had a problem with idling, stuttering, inconsistent RPM, etc. Hopped into my vehicle a few days later with a new LPFP, drove maybe 20 miles and *blam* (red) Check Engine light - Reduced Engine Power. Let it be overnight. Got in the next morning and holy cow, the car started slowly upon ignition, rumbled and grumbled at me, sputtered, RPM very inconsistent, and the telltale signs of unmistakable gas/fuel smell and puffs of white steamy exhaust. Confirmed a new HPLP was needed. Several iterations of the HPFP have been made by Porsche with part numbers superceding part numbers . As I type, I'm waiting for my HPFP to arrive from Germany (!) with 'expedited freight' aka extorsion to get to the top of the list for HPFP, which are sold out in the US and in high demand. So long winded way to share my story but also have you consider the LPFP and or HPFP as the root cause. And to let everyone know they're not available other than directly from Deutschland. PS: I was told by a dealer on the phone (I don't have a dealer within 7 hours drive) that the next thing I should watch out for at my mileage is the transfer case. And to care for it religiously like I replace the oil. Hope that helps!
Last edited by normfly; 06-17-2024 at 08:08 PM.