What is the current state of the 'engine stumble' issue?
08-13-2023, 05:43 PM
#556
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
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
The car does feel more zippy at the lower end of RPM range after the camshaft sensor replacement.
Everything is connected. For example a bad coil gives you a PSM failure message..
Seemingly unrelated things are branched off each other. Sh** code..? who knows. It's VW after all.
Maybe turning off PSM speeds things up during those transition...? Skipping some pathways?
One of these days I am going to bite the bullet and get a DME but I figured I mess around with the cheap stuff like sensors first.
Maybe I will get a used one and reprogram it using PIWIS.
Last edited by Sajan; 08-13-2023 at 05:46 PM.
08-13-2023, 05:54 PM
#557
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?
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?
BTW, my week or so of non-stumbling bliss is apparently over. It was good while it lasted.
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Sajan (08-13-2023)
08-13-2023, 06:14 PM
#558
Sajan - If only we had someone at Porsche that was as dedicated to resolving this problem as you, along with many others, we wouldn't be forced to jump through all these hoops. They are well aware the problem exists, but won't lift a finger to help. (Well, I just lifted a finger to them).
BTW, my week or so of non-stumbling bliss is apparently over. It was good while it lasted.
BTW, my week or so of non-stumbling bliss is apparently over. It was good while it lasted.
1. they fixed it in the 991.2+ cars
2. they think it only affects a small subset of cars
3. the root cause and fix itself is costly
4. it affects a lot more cars but better to keep it hush than have a massive recall for something a good % of owners haven't noticed.
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one-rennlist (09-06-2023)
08-13-2023, 11:14 PM
#559
Look at all the things the DME controls......any of this technically could be the issue..one of these (bolded) is a prerequisite for PSM..
General overview of DME functions
• Thermal management
• Auto Start Stop function
• Variable deceleration fuel cutoff
• Vehicle electrical system recuperation
• Direct fuel injection (DFI)
• Low-pressure fuel supply
• Returnless fuel system
• High-pressure fuel supply (quantity control valve)
• Electronic throttle
• Electronic throttle with idle speed control
• VarioCam Plus (intake camshaft)
• Demand-controlled variable oil pump
• Switchable resonator on the air cleaner housing
• Tuning flap on the intake system (Carrera S only)
• Intake system sound symposer
• Stereo lambda control circuits
• Flap control on the intake system (Carrera S and sports exhaust system)
• Static high-voltage ignition distribution (individual ignition coils with integrated drivers)
• Cylinder-specific knock control (with 2 knock sensors)
• Differential Hall-effect sensor (detects engine speed, reference mark and direction of rotation of the engine
• Pressure sensor on the intake manifold (detects intake manifold pressure and intake air temperature)
• On-board diagnosis for monitoring the emission control system
I will log some data tomm with "Request for large intake valve" (either 0 or 1) on top of the RPMs.
General overview of DME functions
• Thermal management
• Auto Start Stop function
• Variable deceleration fuel cutoff
• Vehicle electrical system recuperation
• Direct fuel injection (DFI)
• Low-pressure fuel supply
• Returnless fuel system
• High-pressure fuel supply (quantity control valve)
• Electronic throttle
• Electronic throttle with idle speed control
• VarioCam Plus (intake camshaft)
• Demand-controlled variable oil pump
• Switchable resonator on the air cleaner housing
• Tuning flap on the intake system (Carrera S only)
• Intake system sound symposer
• Stereo lambda control circuits
• Flap control on the intake system (Carrera S and sports exhaust system)
• Static high-voltage ignition distribution (individual ignition coils with integrated drivers)
• Cylinder-specific knock control (with 2 knock sensors)
• Differential Hall-effect sensor (detects engine speed, reference mark and direction of rotation of the engine
• Pressure sensor on the intake manifold (detects intake manifold pressure and intake air temperature)
• On-board diagnosis for monitoring the emission control system
I will log some data tomm with "Request for large intake valve" (either 0 or 1) on top of the RPMs.
08-14-2023, 09:18 AM
#560
Rennlist Member
I have considered this a minor personality trait and am not letting it bother me. No car is perfect.
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slo_991 (09-12-2023)
08-14-2023, 10:49 AM
#561
Don't start with the 992 ...lol. Stay out of this! I need to believe 992 doesn't have this issue.
Otherwise I am done with Porsche.
Otherwise I am done with Porsche.
08-15-2023, 10:39 AM
#564
08-18-2023, 05:42 PM
#565
Maybe, but it doesn't rule out poorly written software. For example, when a series of analog readings are input to the software, the software usually needs to filter the data, i.e., to take out noise spikes or dips. Not doing that correctly amounts to misinterpreting the information. Of course we will never be able to examine that software.
08-18-2023, 06:11 PM
#566
Maybe, but it doesn't rule out poorly written software. For example, when a series of analog readings are input to the software, the software usually needs to filter the data, i.e., to take out noise spikes or dips. Not doing that correctly amounts to misinterpreting the information. Of course we will never be able to examine that software.
1st gear is smooth as butter. No pause. No stumble.
2-7 is when I feel I pause and stumble.
On heavier throttle, it's a pause. on moderate throttle, it stutters.
Maybe it's a electrical connector issue. Going to take off some of these connectors and spray some deoxit on them..
08-20-2023, 02:59 PM
#568
Any chance it could be a low voltage problem? Alternator going bad? Sub par fuel has been talked about (maybe use Ethanol FREE gas) could that be pulling the timing causing pre-det and sporadic behavior in low RPM ranges?
08-21-2023, 04:13 AM
#569
All tried and tested to no avail..
08-21-2023, 01:53 PM
#570
Three Wheelin'
I have no idea why but mine has been driving perfectly with the stability control turned "off" (yes, I know it's not fully off). I've really enjoyed driving the past couple of weeks.
I forgot to turn off the stability control yesterday and it exhibited the typical stumble symptoms.
I forgot to turn off the stability control yesterday and it exhibited the typical stumble symptoms.