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A sound like pop/gurgle during stumble makes me think about very retarded ignition - combustion not happening well which would makes sense if the engine is required to reduce torque in a very fast manner (with retarded ignition).
I wander if bokh's stumble could be resolved with an DME SW and PSM SW updates.
@Sajan : your stumble has a different root cause but the mechanism (DME applying torque reduction) seems similar to bokh. The 1 million $ question is why the DME is requesting a torque decrease.
Moving forward, has anyone got a car that stumbles that is still CPOed? With all the elements that have been gathered, I suspect mechanics at any dealer or us won't have the means to analyze deeper with a PIWI.
I would suggest to ask if this issue can be reported to Quality department in Germany (PAG) and ask them if they can install a datalogger in the 'stumble' cars with all the DME internal signals (and PSM or any other ECU) to understand where this strange torque decrease requests come from.
A sound like pop/gurgle during stumble makes me think about very retarded ignition - combustion not happening well which would makes sense if the engine is required to reduce torque in a very fast manner (with retarded ignition).
I wander if bokh's stumble could be resolved with an DME SW and PSM SW updates.
@Sajan : your stumble has a different root cause but the mechanism (DME applying torque reduction) seems similar to bokh. The 1 million $ question is why the DME is requesting a torque decrease.
I agree. Considering I notice no difference with PSM off, mine might be a whole different root cause. Also it's one single pop..more and more it feels like a timing issue a not so smooth transition of the variocam because of some sensor feeding slightly erratic data.
The two other times I've heard something similar was more of a higher pitched "ting!"..like a rock hitting a metal bar...that was in march after I replaced my tires. not sure if correlated.
I tried logging timing retardation on all 6 cylinders and that line was straight as an arrow. Either it's too happening too fast for the PIWIS logging sampling rate..or that's not what's happening.
Concerning the audible "pop" associated with my stumble, I found an mp3 recording I made years ago. Mic was near the exhaust during a drive, PSE on. Not sure what to make of it.
Concerning the audible "pop" associated with my stumble, I found an mp3 recording I made years ago. Mic was near the exhaust during a drive, PSE on. Not sure what to make of it.
Ya. same. single pop. pretty loud.
internet search says: If your engine is getting more fuel than it needs, a rich fuel to air ratio is the result. When your car has leftover fuel in the exhaust and the cylinders, that fuel explosively burns and creates a loud popping sound.
I went for an extended drive last night. I switched the PSM off and then back on, and let the throttle body do its adaptation while the key was in the ignition (engine not running). Zero stumble, car drove brilliantly.
The other strange correlation that I am noticing is that it seems to run better in cooler temps (ie, last night was about 15 C). This might explain why when I changed my throttle pedal back in the spring, I thought it had fixed the issue.
I tried logging timing retardation on all 6 cylinders and that line was straight as an arrow. Either it's too happening too fast for the PIWIS logging sampling rate..or that's not what's happening.
I would assume it is sampling logging rate which is too slow. If you feel the stumble and hear the pop, then something is happening on the DME side.
Other items I thought about lately :
1. Do you have any DTCs in the DME? Does the PIWIS tells the status of the DTC such as : permanent, pending etc.
2. Do you have a way to read IUPR values (In Use Performance Ratio) with the PIWIS : IUPR basically means how often some diagnostic strategies are carried out provided the engine was run in the conditions where the diagnostic strategies can operate (to detect a faulty actuator for instance).
The numerator of the IUPR increases every time a diagnostic is carried out and the denominator increases every time the conditions for the diagnostic to occur are met.
It would be interesting to see if the IUPR values increases after a (or several) stumble(s) occur(s). If one of the diagnostic consists in the valve lift or the valve timing being changed to check if the corresponding solenoid/actuator still performs correctly, that could create a stumble.
This will create an inconvenience for the customer (the stumble) but it is required to ensure that the actuator of the engine works normally (and cannot increase pollutant emissions abnormally).
These IUPR values must be above a minimum value (required by law) which means the DME can decide it must activate these diagnostics to ensure the IUPR value is high enough (to comply with law).
Since complying to the requirements of the law is more important than an "inconvenience" for the driver (the stumble), that might explain why first MY cars can have a tendency to stumble. Maybe the engineers found a way later to mitigate this issue and the stumble was solved by SW in the later MY.
post #463, but here is my work order of items completed for reference. Hope this helps
Had the AMC0 recall done in June and it didn't make a diff.
Originally Posted by Watson
I would assume it is sampling logging rate which is too slow. If you feel the stumble and hear the pop, then something is happening on the DME side.
Other items I thought about lately :
1. Do you have any DTCs in the DME? Does the PIWIS tells the status of the DTC such as : permanent, pending etc.
2. Do you have a way to read IUPR values (In Use Performance Ratio) with the PIWIS : IUPR basically means how often some diagnostic strategies are carried out provided the engine was run in the conditions where the diagnostic strategies can operate (to detect a faulty actuator for instance).
The numerator of the IUPR increases every time a diagnostic is carried out and the denominator increases every time the conditions for the diagnostic to occur are met.
It would be interesting to see if the IUPR values increases after a (or several) stumble(s) occur(s). If one of the diagnostic consists in the valve lift or the valve timing being changed to check if the corresponding solenoid/actuator still performs correctly, that could create a stumble.
This will create an inconvenience for the customer (the stumble) but it is required to ensure that the actuator of the engine works normally (and cannot increase pollutant emissions abnormally).
These IUPR values must be above a minimum value (required by law) which means the DME can decide it must activate these diagnostics to ensure the IUPR value is high enough (to comply with law).
Since complying to the requirements of the law is more important than an "inconvenience" for the driver (the stumble), that might explain why first MY cars can have a tendency to stumble. Maybe the engineers found a way later to mitigate this issue and the stumble was solved by SW in the later MY.
No codes. ever.
not sure how to figure out IUPR values.
So y'all can cross off camshaft position sensors from the list...maybe not fully..
I replaced both sides with new Bosch ones. The ones that were in there were from Oct 2013. it was relatively easy. One screw. Hardest part is moving the small ratchet in there to loosen it. It said 7.5 lb ft of torque but I didn't bother using a torque wrench for that..lol.
Now I've only done about 3 test drives since then but the stumble is now only noticeable in 5th gear.. 2,3,5,6 feel a tad bit smoother. I also noticed my deviation changed for bank 1. This is the same bank that adjustment angle constantly fluctuates. BEFORE AFTER
Had the AMC0 recall done in June and it didn't make a diff.
It's strange that some of these "fixes" work for some but not others...Some things are just worth taking a shot at. Is it a combination of the items I replaced and the AMCO recall that made mine better? IDK but it appears for now that it's worked out in my case. I let a friend borrow my 991 for the weekend a couple weeks ago and he stated that he felt no stumble while driving it around town and a couple spirited drives. He did know about my battle with it and the parts I've swapped out. Is it any 1 thing that "fixes it" or the combination of worn out components.
It's strange that some of these "fixes" work for some but not others...Some things are just worth taking a shot at. Is it a combination of the items I replaced and the AMCO recall that made mine better? IDK but it appears for now that it's worked out in my case. I let a friend borrow my 991 for the weekend a couple weeks ago and he stated that he felt no stumble while driving it around town and a couple spirited drives. He did know about my battle with it and the parts I've swapped out. Is it any 1 thing that "fixes it" or the combination of worn out components.
This was my thought was well yesterday.
For example, from reading through the stumble threads, someone said don't bother with the crankshaft sensor.
But when I was browsing the ends of internet, I saw our fellow stumbler pfan replaced it back in 2014 relating to a stall? https://rennlist.com/forums/991/8649...ont-start.html
I am going to change this out next. Figured for 30 bucks, why not..?
We really need to look at this from a holistic perspective. It's not a single part. It's a suite of sensors/solenoids the DME is manipulating. When one is slightly out of whack, the other compensates. Maybe fellow stumblers have changed many things during their journey. Maybe I haven't changed something yet that others have which is why the PSM off trick is not working for me.
The more I drive it, the more I realize it's at two specific transition points where this stumble is felt. Right around 2200 and then at 2800. At heavier throttle, it presents itself as pauses in torque/power delivery. At slight to moderate load it stutters/stumbles.
It's like going over potholes. Do it slow and you feel each one....if you go fast enough it's bumpy but "smoother". Whatever the DME is programmed to do, the engine is not doing quick enough or seamlessly enough.
I am going to see if I can put a multimeter on the connectors to the camshaft solenoids. It's bugging me that I don't hear them activate when I do the drive link tests unless I repeat the test 8-12 times..if only I had a non-stumble car to test with..
It's also bugging me that one bank's adjustment angle fluctuates a lot more.
Something else I notice is the stutter from a stop to 1st gear but I just assumed this was PDK behavior ..maybe not?
This was my thought was well yesterday.
For example, from reading through the stumble threads, someone said don't bother with the crankshaft sensor.
But when I was browsing the ends of internet, I saw our fellow stumbler pfan replaced it back in 2014 relating to a stall? https://rennlist.com/forums/991/8649...ont-start.html
I am going to change this out next. Figured for 30 bucks, why not..?
We really need to look at this from a holistic perspective. It's not a single part. It's a suite of sensors/solenoids the DME is manipulating. When one is slightly out of whack, the other compensates. Maybe fellow stumblers have changed many things during their journey. Maybe I haven't changed something yet that others have which is why the PSM off trick is not working for me.
The more I drive it, the more I realize it's at two specific transition points where this stumble is felt. Right around 2200 and then at 2800. At heavier throttle, it presents itself as pauses in torque/power delivery. At slight to moderate load it stutters/stumbles.
It's like going over potholes. Do it slow and you feel each one....if you go fast enough it's bumpy but "smoother". Whatever the DME is programmed to do, the engine is not doing quick enough or seamlessly enough.
I am going to see if I can put a multimeter on the connectors to the camshaft solenoids. It's bugging me that I don't hear them activate when I do the drive link tests unless I repeat the test 8-12 times..if only I had a non-stumble car to test with..
It's also bugging me that one bank's adjustment angle fluctuates a lot more.
Something else I notice is the stutter from a stop to 1st gear but I just assumed this was PDK behavior ..maybe not?
Totally agree.
Side note: Seems trivial but, before I had the AMCO recall, I did adjust my seat a touch more forward so that my entire foot is in better contact with the gas pedal after I replaced it (vs the heal toe kind of placement) It did have a positive effect around the stumble RPM's of 2600-3000 for me. I think the gas pedal is rather "touchy" IMHO. Before I did this I felt like my foot was "pointing" vs pushing it down if that makes sense..? This is my first Pcar, so the angle of the seat in relation to the pedals was far different from what I was used to with my previous Audi's = drivers seated position
08-09-2023, 03:08 PM
