What is the current state of the 'engine stumble' issue?
08-06-2023, 04:49 PM
#526
The following 2 users liked this post by pfan:
one-rennlist (09-06-2023),
Sajan (08-06-2023)
08-06-2023, 06:31 PM
#527
OK, that is interesting. Do you have your PSM off permanently or did you do the PSM on/off trick used by bokh? Hopefully duxsi and Sajan can come to the same findings.
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
The torque ultimately delivered by the engine comes from different torque requests : the driver requests torque via the gas pedal, the A/C can request additional torque to the engine, the PSM can also request engine torque decrease etc.
The DME (the engine ECU) takes all these torque requests into consideration before delivering the final engine torque.
From my limited understanding, the traction control part of the PSM can also request engine torque decrease by retarding the ignition (as seen in some of Sajan's previous log) - maybe the air mass going into the engine is also decreased if retarding the ignition is not enough to decrease the engine torque as per PSM request.
So if there is no more stumble when PSM is off, it means that there may be nothing wrong with the engine itself (HW or SW) since the DME is only "reacting" to a (strange) torque request from another ECU (allegedly the PSM ECU).
Now, why would the PSM send funky torque decrease requests to the DME?
- problem with the PSM SW (bugs etc) or calibration. Maybe ironed out in later PSM SW releases? Could explain why 991.1 GTS i.e. MY 15/16 do not have them (is this even a fact or not?)? I have not experienced any stumble on my '16 991.1 GTS Targa 7MT but to be honest, I have not really looked for it.
- incompatibility between PSM SW and DME SW : maybe one is outdated compared to the other one,
- underlying HW issues related to PSM SW input signals (sensors, harness),
- PSM ECU HW.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
- Do the people who have stumble issue have upgraded to the latest version of PSM SW and DME SW or not?
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
The torque ultimately delivered by the engine comes from different torque requests : the driver requests torque via the gas pedal, the A/C can request additional torque to the engine, the PSM can also request engine torque decrease etc.
The DME (the engine ECU) takes all these torque requests into consideration before delivering the final engine torque.
From my limited understanding, the traction control part of the PSM can also request engine torque decrease by retarding the ignition (as seen in some of Sajan's previous log) - maybe the air mass going into the engine is also decreased if retarding the ignition is not enough to decrease the engine torque as per PSM request.
So if there is no more stumble when PSM is off, it means that there may be nothing wrong with the engine itself (HW or SW) since the DME is only "reacting" to a (strange) torque request from another ECU (allegedly the PSM ECU).
Now, why would the PSM send funky torque decrease requests to the DME?
- problem with the PSM SW (bugs etc) or calibration. Maybe ironed out in later PSM SW releases? Could explain why 991.1 GTS i.e. MY 15/16 do not have them (is this even a fact or not?)? I have not experienced any stumble on my '16 991.1 GTS Targa 7MT but to be honest, I have not really looked for it.
- incompatibility between PSM SW and DME SW : maybe one is outdated compared to the other one,
- underlying HW issues related to PSM SW input signals (sensors, harness),
- PSM ECU HW.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
- Do the people who have stumble issue have upgraded to the latest version of PSM SW and DME SW or not?
08-06-2023, 06:32 PM
#528
Has anyone isolated this 'stumble' issue to particular variant of the 991.1? Do GTS cars with the X51 Powerkit exhibit the same behaviour? Do the GT3's have the same issue? I would assume these are running all different DME units as they are all different in engine internals, intake etc. but I could be wrong about that. Trying to rule out the previous comments about the issue being related to the DME and or factory programming. Does anyone know of a car(s) that may be equipped with and aftermarket custom DME that has this tuned out or is strictly related to emissions as many have surmised? Thoughts??
The DME is the same part number for almost all the variants 981/991.1 cars....except the GT3 it seems.
Maybe it's the PSM module??
Also the other form said tune from Cobb didn't make a diff.
OK, that is interesting. Do you have your PSM off permanently or did you do the PSM on/off trick used by bokh? Hopefully duxsi and Sajan can come to the same findings.
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
The torque ultimately delivered by the engine comes from different torque requests : the driver requests torque via the gas pedal, the A/C can request additional torque to the engine, the PSM can also request engine torque decrease etc.
The DME (the engine ECU) takes all these torque requests into consideration before delivering the final engine torque.
From my limited understanding, the traction control part of the PSM can also request engine torque decrease by retarding the ignition (as seen in some of Sajan's previous log) - maybe the air mass going into the engine is also decreased if retarding the ignition is not enough to decrease the engine torque as per PSM request.
So if there is no more stumble when PSM is off, it means that there may be nothing wrong with the engine itself (HW or SW) since the DME is only "reacting" to a (strange) torque request from another ECU (allegedly the PSM ECU).
Now, why would the PSM send funky torque decrease requests to the DME?
- problem with the PSM SW (bugs etc) or calibration. Maybe ironed out in later PSM SW releases? Could explain why 991.1 GTS i.e. MY 15/16 do not have them (is this even a fact or not?)? I have not experienced any stumble on my '16 991.1 GTS Targa 7MT but to be honest, I have not really looked for it.
- incompatibility between PSM SW and DME SW : maybe one is outdated compared to the other one,
- underlying HW issues related to PSM SW input signals (sensors, harness),
- PSM ECU HW.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
- Do the people who have stumble issue have upgraded to the latest version of PSM SW and DME SW or not?
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
The torque ultimately delivered by the engine comes from different torque requests : the driver requests torque via the gas pedal, the A/C can request additional torque to the engine, the PSM can also request engine torque decrease etc.
The DME (the engine ECU) takes all these torque requests into consideration before delivering the final engine torque.
From my limited understanding, the traction control part of the PSM can also request engine torque decrease by retarding the ignition (as seen in some of Sajan's previous log) - maybe the air mass going into the engine is also decreased if retarding the ignition is not enough to decrease the engine torque as per PSM request.
So if there is no more stumble when PSM is off, it means that there may be nothing wrong with the engine itself (HW or SW) since the DME is only "reacting" to a (strange) torque request from another ECU (allegedly the PSM ECU).
Now, why would the PSM send funky torque decrease requests to the DME?
- problem with the PSM SW (bugs etc) or calibration. Maybe ironed out in later PSM SW releases? Could explain why 991.1 GTS i.e. MY 15/16 do not have them (is this even a fact or not?)? I have not experienced any stumble on my '16 991.1 GTS Targa 7MT but to be honest, I have not really looked for it.
- incompatibility between PSM SW and DME SW : maybe one is outdated compared to the other one,
- underlying HW issues related to PSM SW input signals (sensors, harness),
- PSM ECU HW.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
- Do the people who have stumble issue have upgraded to the latest version of PSM SW and DME SW or not?
My DME has a last programmed date from June 2023 because of the emissions recall. I believe both the DME and PDK is reprogrammed for that campaign.
I logged the PSM wheel sensors and they were beautifully linear. No dips. Nothing.
Last edited by Sajan; 08-06-2023 at 06:36 PM.
08-06-2023, 09:14 PM
#529
OK, that is interesting. Do you have your PSM off permanently or did you do the PSM on/off trick used by bokh? Hopefully duxsi and Sajan can come to the same findings.
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
My previous 997.2 was a massive stumbler. If it happened to stumble in a tunnel there was a very distinctive "pop", especially with the PSE selected.
08-06-2023, 09:52 PM
#530
I've mainly been driving with the PSM off, however, I've also seen improvement with it on after having it off within the previous day or so. Mysterious as to why it helps some but not others.
My previous 997.2 was a massive stumbler. If it happened to stumble in a tunnel there was a very distinctive "pop", especially with the PSE selected.
My previous 997.2 was a massive stumbler. If it happened to stumble in a tunnel there was a very distinctive "pop", especially with the PSE selected.
what clue does this give us?
not sure if related:
I remember reading something about the Exhaust gas recirculation is done/achieved by the valve lift?
is turning off the PSM fixing some kind of voltage issue caused by a bad sensor?
I have seen all sorts of faults on various systems just because of a bad battery. My point being…the psm being off is fixing something else? Just thinking out loud at this point :-)
08-06-2023, 10:00 PM
#531
Popping makes me think you've temporarily lost ignition.
08-06-2023, 10:41 PM
#532
OK, that is interesting. Do you have your PSM off permanently or did you do the PSM on/off trick used by bokh? Hopefully duxsi and Sajan can come to the same findings.
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
The torque ultimately delivered by the engine comes from different torque requests : the driver requests torque via the gas pedal, the A/C can request additional torque to the engine, the PSM can also request engine torque decrease etc.
The DME (the engine ECU) takes all these torque requests into consideration before delivering the final engine torque.
From my limited understanding, the traction control part of the PSM can also request engine torque decrease by retarding the ignition (as seen in some of Sajan's previous log) - maybe the air mass going into the engine is also decreased if retarding the ignition is not enough to decrease the engine torque as per PSM request.
So if there is no more stumble when PSM is off, it means that there may be nothing wrong with the engine itself (HW or SW) since the DME is only "reacting" to a (strange) torque request from another ECU (allegedly the PSM ECU).
Now, why would the PSM send funky torque decrease requests to the DME?
- problem with the PSM SW (bugs etc) or calibration. Maybe ironed out in later PSM SW releases? Could explain why 991.1 GTS i.e. MY 15/16 do not have them (is this even a fact or not?)? I have not experienced any stumble on my '16 991.1 GTS Targa 7MT but to be honest, I have not really looked for it.
- incompatibility between PSM SW and DME SW : maybe one is outdated compared to the other one,
- underlying HW issues related to PSM SW input signals (sensors, harness),
- PSM ECU HW.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
- Do the people who have stumble issue have upgraded to the latest version of PSM SW and DME SW or not?
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
The torque ultimately delivered by the engine comes from different torque requests : the driver requests torque via the gas pedal, the A/C can request additional torque to the engine, the PSM can also request engine torque decrease etc.
The DME (the engine ECU) takes all these torque requests into consideration before delivering the final engine torque.
From my limited understanding, the traction control part of the PSM can also request engine torque decrease by retarding the ignition (as seen in some of Sajan's previous log) - maybe the air mass going into the engine is also decreased if retarding the ignition is not enough to decrease the engine torque as per PSM request.
So if there is no more stumble when PSM is off, it means that there may be nothing wrong with the engine itself (HW or SW) since the DME is only "reacting" to a (strange) torque request from another ECU (allegedly the PSM ECU).
Now, why would the PSM send funky torque decrease requests to the DME?
- problem with the PSM SW (bugs etc) or calibration. Maybe ironed out in later PSM SW releases? Could explain why 991.1 GTS i.e. MY 15/16 do not have them (is this even a fact or not?)? I have not experienced any stumble on my '16 991.1 GTS Targa 7MT but to be honest, I have not really looked for it.
- incompatibility between PSM SW and DME SW : maybe one is outdated compared to the other one,
- underlying HW issues related to PSM SW input signals (sensors, harness),
- PSM ECU HW.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
- Do the people who have stumble issue have upgraded to the latest version of PSM SW and DME SW or not?
I’ve had more than a week of daily driving without any stumble and without having to touch the PSM button. Doing the trick a few times last week cured the car completely. Will see how long this lasts…
The following users liked this post:
Sajan (08-06-2023)
08-07-2023, 09:57 AM
#533
2016 991.1 when driving with PSM off the stumble does not exist any longer.
I have been testing for about 2 weeks and not one incidence!
Much happier with the engine performance currently.
Looks like I will be driving old school seat of the pants traction control unless road conditions dictate otherwise!!!
I have been testing for about 2 weeks and not one incidence!
Much happier with the engine performance currently.
Looks like I will be driving old school seat of the pants traction control unless road conditions dictate otherwise!!!
The following users liked this post:
Sajan (08-07-2023)
08-07-2023, 12:47 PM
#534
OK, that is interesting. Do you have your PSM off permanently or did you do the PSM on/off trick used by bokh? Hopefully duxsi and Sajan can come to the same findings.
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
The torque ultimately delivered by the engine comes from different torque requests : the driver requests torque via the gas pedal, the A/C can request additional torque to the engine, the PSM can also request engine torque decrease etc.
The DME (the engine ECU) takes all these torque requests into consideration before delivering the final engine torque.
From my limited understanding, the traction control part of the PSM can also request engine torque decrease by retarding the ignition (as seen in some of Sajan's previous log) - maybe the air mass going into the engine is also decreased if retarding the ignition is not enough to decrease the engine torque as per PSM request.
So if there is no more stumble when PSM is off, it means that there may be nothing wrong with the engine itself (HW or SW) since the DME is only "reacting" to a (strange) torque request from another ECU (allegedly the PSM ECU).
Now, why would the PSM send funky torque decrease requests to the DME?
- problem with the PSM SW (bugs etc) or calibration. Maybe ironed out in later PSM SW releases? Could explain why 991.1 GTS i.e. MY 15/16 do not have them (is this even a fact or not?)? I have not experienced any stumble on my '16 991.1 GTS Targa 7MT but to be honest, I have not really looked for it.
- incompatibility between PSM SW and DME SW : maybe one is outdated compared to the other one,
- underlying HW issues related to PSM SW input signals (sensors, harness),
- PSM ECU HW.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
- Do the people who have stumble issue have upgraded to the latest version of PSM SW and DME SW or not?
The fact that bokh had the stumble came back immediately when switching from PSM off to on is remarkable.
The torque ultimately delivered by the engine comes from different torque requests : the driver requests torque via the gas pedal, the A/C can request additional torque to the engine, the PSM can also request engine torque decrease etc.
The DME (the engine ECU) takes all these torque requests into consideration before delivering the final engine torque.
From my limited understanding, the traction control part of the PSM can also request engine torque decrease by retarding the ignition (as seen in some of Sajan's previous log) - maybe the air mass going into the engine is also decreased if retarding the ignition is not enough to decrease the engine torque as per PSM request.
So if there is no more stumble when PSM is off, it means that there may be nothing wrong with the engine itself (HW or SW) since the DME is only "reacting" to a (strange) torque request from another ECU (allegedly the PSM ECU).
Now, why would the PSM send funky torque decrease requests to the DME?
- problem with the PSM SW (bugs etc) or calibration. Maybe ironed out in later PSM SW releases? Could explain why 991.1 GTS i.e. MY 15/16 do not have them (is this even a fact or not?)? I have not experienced any stumble on my '16 991.1 GTS Targa 7MT but to be honest, I have not really looked for it.
- incompatibility between PSM SW and DME SW : maybe one is outdated compared to the other one,
- underlying HW issues related to PSM SW input signals (sensors, harness),
- PSM ECU HW.
Other questions :
- Are all stumble issues limited to a certain MY(12, 13, 14)?
- Do the people who have stumble issue have upgraded to the latest version of PSM SW and DME SW or not?
• ABS (Anti-lock Brake System)
• EDTC (Engine Drag Torque Control) - Adjusts engine speed when the acceleration pedal is released to prevent slip on the drive wheels (this slip can be produced by the engine's brake force)
• ASR (Anti Slip Regulation)
• ABD (Automatic Brake Differential)
• EBD (Electronic Brake-force Distribution)
• Enhanced braking readiness through pre-filling of the brake system
• Brake assist function: generates the brake pressure needed for maximum deceleration when emergency braking is detected
• Standstill management: Auto-hold function in conjunction with the electric parking brake
• Driving dynamics control: wheel-specific braking intervention to ensure driving stability
Here's some info about the DME:
The high-performance electronic engine control unit EMS SDI 9 from Continental is used for the 911 Carrera (991) engines. This control unit has been specially designed to meet the requirements for use of direct fuel injection (DFI) and VarioCam Plus. Of particular significance here is control of the injectors, which are central elements of the direct fuel injection system. The engine control also controls the throttle position (electronic throttle) as this is a prerequisite for the Porsche Stability Management (PSM) system installed as standard.
08-07-2023, 01:07 PM
#535
Thanks Sajan, excellent information.
I have tested the ABS feature a dozen times or so with PSM OFF and I could discern no difference in braking distance or overall feel as a side note.
Perhaps there are subtle enhancements as mentioned, wanted to see if the ABS functionality was disabled or not.
Just adding another data point.
I have tested the ABS feature a dozen times or so with PSM OFF and I could discern no difference in braking distance or overall feel as a side note.
Perhaps there are subtle enhancements as mentioned, wanted to see if the ABS functionality was disabled or not.
Just adding another data point.
08-07-2023, 01:18 PM
#536
Thanks Sajan, excellent information.
I have tested the ABS feature a dozen times or so with PSM OFF and I could discern no difference in braking distance or overall feel as a side note.
Perhaps there are subtle enhancements as mentioned, wanted to see if the ABS functionality was disabled or not.
Just adding another data point.
I have tested the ABS feature a dozen times or so with PSM OFF and I could discern no difference in braking distance or overall feel as a side note.
Perhaps there are subtle enhancements as mentioned, wanted to see if the ABS functionality was disabled or not.
Just adding another data point.
" If you prefer an ever sportier drive, PSM can be switched off. For your safety, however, PSM remains set to intervene if the vehicle is braked and ABS assistance is required. ABS and ABD remain switched on at all times."
08-07-2023, 02:42 PM
#537
Rennlist Member
The stumble is usually very subtle, and only occurs under light to moderate throttle. (I'm sure there are some other hesitations, etc, that occur under higher throttle applications). Generally, the only indication is seat of the pants, or possibly aurally from an occasional slight exhaust note change, or "pop".
08-07-2023, 03:12 PM
#538
Something that has peaked my interest is the actual camshaft angle values under camshaft timing.
I don't have a normal car to compare it to but I am curious if the two angle values are supposed to be the same with each other and also to the setpoint angle.
I don't have a normal car to compare it to but I am curious if the two angle values are supposed to be the same with each other and also to the setpoint angle.
08-09-2023, 02:11 PM
#539
Ever since I changed the two camshaft solenoids, I've heard the "pop" during the stumble ...twice now in the last 5 or 6 drives. I don't remember hearing it this often but I also wasn't trying to make this stumble happen either..
Coincidence or clue? not sure.
Coincidence or clue? not sure.
08-09-2023, 03:07 PM
#540
Backfire pop and mechanical?