6L80 behind a Mercedes turbodiesel - shift flare 5-6

Hi all,

I have a Mercedes turbodiesel running with a 2015 6L80 behind and a PCS TCM-2650 sending the relevant torque, TPS, and RPM signals to the 6L80.

Everything works quite well, but there's one problem: massive shift flare between 5th (TCC locked) to 6th:

1) 5th gear (TCC locked, all is well)
2) TCC unlocks, RPM flares way up
3) Shift to 6th takes place
4) TCC locks shortly after

See the 2:59:206 mark in the attached log.

The PCS unit is set up to signal a shift event to engine controller so it can pull fuel as a method of torque management. This function works fine in 4-5 upshifts, but for some reason not 5-6th.

Are there some parameters that control whether or not the 6L80 requests torque management during a shift?

Or is this just a problem any time there's an up-shift from a locked gear?

Thanks for any help in advance.

Hi there Anothernord, I have just finished putting a 6L80E behind a GEN3 Ls1 in a Holden Cross 8 Crewman, also using theTCM-2650 as the base control. I am just stating to try and understand the A6 programming, to say it is complicated is an understatement and adding in the TCM 2650 adds another level. I am having some flaring issues 1/2 2/3 shift, the rest off the shifts feel acceptable. Where I am at so far is that I can see, on the2/3 shift that the PC SOL4 drops very early in the shift and the PC SOl 2 starts to activate then drops 85 kpa before raising again, I am reasonably confident that this is causing the corresponding flare. If I look at your log you 2/3 clutch engagement looks like what I would expect, one clutch goes off and the next is well on its way to applying. Where as at you 5/6 change the cross over point is midway through the shift. What this means at this point in time I am still trying to work out, but after I read the following form specifically Chris's explanation I am going to start to test some different pressures to see if I can move the shift points. The other thing I need to try and do is get the adaptive function working, I figure this is in the base O/S that HP tuners cant access. I will let you know if I have any luck.
https://forum.hptuners.com/showthrea...Max+2-3+volume
HP Tuners Owner

Chris@HPTuners's AvatarJoin Date
Mar 2003
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4,864
the oncoming pressure preset is the base point for the oncoming (applying) clutch during the shift

the offgoing pressure preset is the same for the offgoing (releasing) clutch.

the volume adapt is used to calculate the fill time becuase around the time the clutch is estimated to be full the offgoing clutch pressure is dropped. It also provides feedback to the logic that pressure related issues can be identified becuase the clutch is "full". ie. there is no point adapting offgoing pressure if the symptom of the poor shift relates to the oncoming clutch being overfilled.

they are all adapted depending on how the shift actually executed and whether torque and throttle indicate it was a powered or unpowered shift.

Some examples:
- if flare occurred early in an upshift it means the offgoing pressure was too low to hold the old gear while the new clutch is applying.
- in the case that the new gear engages early it could be an overfill condition before the offgoing pressure release occurs so an oncoming volume adapt might be necessary
- if a flare occurs after the oncoming clutch is full and the offgoing clutch pressure is dropping it means the oncoming pressure is too low
- if the new gear engages late and a flare occurred it means the oncoming didn't have enough pressure or volume or both

there are complicated aritration algorithms that identify all kinds of timings, torque rampings and flare identification, that influence either the oncoming or offgoing pressure or the oncoming volume.

if you have mofied your trans to include more clutch packs or thicker materials, then likely you will need to reduce the volumes. you can mess with the adapts if you specifically can see flaring or any other symptoms of shift binding etc.

In general so long as you have the starting points close the code does a great job of adapting.

Hope that helps,

Quote:

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Originally Posted by anothernord

Hi all,

I have a Mercedes turbodiesel running with a 2015 6L80 behind and a PCS TCM-2650 sending the relevant torque, TPS, and RPM signals to the 6L80.

Everything works quite well, but there's one problem: massive shift flare between 5th (TCC locked) to 6th:

---

Would you mind giving this a try please?

Attachment 109918

During the 5th to 6th shift the TCC is active but just doesn't have enough pressure going to it to keep it locked.

Quote:

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Originally Posted by CWG66

Hi there Anothernord, I have just finished putting a 6L80E behind a GEN3 Ls1 in a Holden Cross 8 Crewman, also using theTCM-2650 as the base control

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Would you mind trying this? So many things have been adjusted in your posted tune. Please perform a KOEO adapt reset / preset with the scanner after flashing. This will shift funny for a drive cycle or 2. Don't be hard on it. Turn the car off so the adapt values are updated for next drive cycle.

Add input shaft and trans slip PIDs to your channel list.

Attachment 109920

Thanks hjtrbo Appreciate the input, I will have a look.

Hi Anothernord Can you please tell me which output from the PCS2655 you are using to signal the engine controller? Thanks

Quote:

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Originally Posted by CWG66

Thanks hjtrbo Appreciate the input, I will have a look.

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No worries, the trans should adapt that shift. I did read somewhere about a min trans temp is required for the adapts to take but I can't say that verbatim and can't remember where I read it so take it with a grain of salt. Another thing you can do is increase that particular shifts base shift pressure by 10% at a time as a part of fault finding to see if it sorts it out. Or adjust up your TPS to torque map in the 2650.

Quote:

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Originally Posted by CWG66

Hi Anothernord Can you please tell me which output from the PCS2655 you are using to signal the engine controller? Thanks

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Hello, sorry for the delay. I was using PWM9 to signal the engine ECU to cut fuel, but for some reason the TCM 2650 software is buggy and won't enable it for the 5-6 shift. I abandoned that and it seems to work ok anyway.

Quote:

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Originally Posted by hjtrbo

Would you mind giving this a try please?

Attachment 109918

During the 5th to 6th shift the TCC is active but just doesn't have enough pressure going to it to keep it locked.

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Hi there, thanks for the the file. I finally got the chance to try it out and it definitely helps a ton. I believe that I tried editing the pressure table before, but I may have been fighting a software bug that I have read others having where the controller doesn't look at the PCA pressure table. It seems to be fixed in your file, however.