XHP DCT - Experience Thread
- Thread starter JohnDaviz
- Start date
This is what causes DCT burble on other cars but isnt as prevalent on BMW N54 DCTs. Its designed to make the shift smoother but it does so at the expense of the clutches. The shorter the shift and the lower the intervention the better.
edit per Kens comments this is incorrect
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TQ Limit 4 is not normal during shift. There is a bug in the IJE0S and INA0S ROM that causes torque limit 4 on shift when you change the boost ceiling from 1.28 bar. For this reason all new MHD OTS maps remain 1.28 bar because it causes shift delay on the DCT cars. We can have @jyamona look into why, but I want to be clear that torque limit 4 is not normal. I'm personally running up to 30 psi with my Z4 35is, I do not have torque limit 4 on shift because I keep my boost ceiling at 1.28 bar and scale with a 5 bar sensor to achieve a 40 psi boost target (ceiling).
So Ken if it’s not that one can you please point out which one of the torque limiters is normal for shift intervention?
Also I take it you excluded IKMOS DCT because it’s not a common configuration or is it not a problem on IKMOS DCT?
You shouldn't seen any Torque Limit Active value at shift. IKM0S was never sold with DCT.
I'm sure the bug is in IKM0S for DCT also. This is a good question for @jyamona. More than likely the boost ceiling in your map is set higher than 1.28 bar.
I don´t have raised boost ceiling and running stock sensor. Still got Tq Limi 4 once.
18psi but I don´t think that this is relevant.
I never had Tq Limit Active 4 occurred during my custom tunes.
Now found it with xhp the first time in one log. I shifted at 3k Rpm and torque actual dropped from 380 to 183.
@carabuser
You stated that stock tq reduction on your z4 is 175. Can you tell if this also is the case on a 335i / is?
I got the tq lim 4 when tq actual dropped from 380 to 183. That is a tq reduction of 197.
During the log I set tq reduction to 300 within the xhp flash settings. Could it be that this may be the reason for the event?
How was it in your log when it happened?
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Update on this. Just changed the tyres and it's getting grip again that's obviously having an effect to the kick out on the back and getting power down. Definetly feels abit quicker but not so fun any more ha ha. But I really don't remember doing this on any other tyres. Same tyres same car aswell. Been great fun. Mixture of the mhd/xhp
Attachments
I've uploaded the page about DME torque limits. Props to RSL for pointing it out to me.
Tq Limit 4 appears on the stock tune during shifts so is not purely the results of a non stock configuration and from looking at the definition in the "Funktionsdokumentation" it looks clear that torque limits are part of normal operation. It may also be an issue with the boost ceiling but for all my experiences my ceiling has been kept at 1.28 and I don't use any scaling so my peak target boost is pegged at 18.5PSI~.
Tq Limits are normal during certain shifts and depend entirely on the shift scenario. As you can see in the PDF there's limit values for stability control, traction control, gearshift up and down, shift down to prevent stall, rev limit, speed limit, temperature limits and plenty more I can't discern from German acronyms.
Regarding limit 4 being normal during WOT shifts on tuned cars. I have a huge heap of logs that show when reporting torque closer to stock (700nm and below at my level) during a WOT shift torque limit 4 is active but when reporting above 700nm torque limit 4 is almost never seen. I certainly agree with Clemens that sometimes the tq limit signal is too fast for the 10Hz MHD logging but not sure I agree that it is always active. And when reporting torque at stock levels the limit can be active for 2 MHD scans which is something I never see at higher reported torque.
Reported torque also has an influence on timing pulls in the DME outside of shift scenarios but I have no way of monitoring the status words as I can't find their RAM addresses in INA0S. For example if you keep your DCT in manual and in a high gear and try going anywhere over 50% pedal below 3k you'll notice the engine pulls a load of timing but only if you report higher than stock torque levels. I found the tables in the DME responsible for this and just zeroed them out and the problem goes away.
Here's some logs. I was testing the timing limit tables on boost onset so there's a few things going but you can see what I typically see with torque limit 4 only being active with lower reported torque:
Low torque: https://datazap.me/u/rich/v175?log=0&data=3-5-22-26-27-28&solo=27&zoom=91-172
Higher torque: https://datazap.me/u/rich/v173?log=0&data=3-6-22-26-27-28&solo=27
Tq Limit 4 appears on the stock tune during shifts so is not purely the results of a non stock configuration and from looking at the definition in the "Funktionsdokumentation" it looks clear that torque limits are part of normal operation. It may also be an issue with the boost ceiling but for all my experiences my ceiling has been kept at 1.28 and I don't use any scaling so my peak target boost is pegged at 18.5PSI~.
Tq Limits are normal during certain shifts and depend entirely on the shift scenario. As you can see in the PDF there's limit values for stability control, traction control, gearshift up and down, shift down to prevent stall, rev limit, speed limit, temperature limits and plenty more I can't discern from German acronyms.
Regarding limit 4 being normal during WOT shifts on tuned cars. I have a huge heap of logs that show when reporting torque closer to stock (700nm and below at my level) during a WOT shift torque limit 4 is active but when reporting above 700nm torque limit 4 is almost never seen. I certainly agree with Clemens that sometimes the tq limit signal is too fast for the 10Hz MHD logging but not sure I agree that it is always active. And when reporting torque at stock levels the limit can be active for 2 MHD scans which is something I never see at higher reported torque.
Reported torque also has an influence on timing pulls in the DME outside of shift scenarios but I have no way of monitoring the status words as I can't find their RAM addresses in INA0S. For example if you keep your DCT in manual and in a high gear and try going anywhere over 50% pedal below 3k you'll notice the engine pulls a load of timing but only if you report higher than stock torque levels. I found the tables in the DME responsible for this and just zeroed them out and the problem goes away.
Here's some logs. I was testing the timing limit tables on boost onset so there's a few things going but you can see what I typically see with torque limit 4 only being active with lower reported torque:
Low torque: https://datazap.me/u/rich/v175?log=0&data=3-5-22-26-27-28&solo=27&zoom=91-172
Higher torque: https://datazap.me/u/rich/v173?log=0&data=3-6-22-26-27-28&solo=27
@Sbrach would know more about the codes that show up on the E series N55, but you also have three channels to monitor where n54 is only one. I could be completely wrong, but I do know that my car doesn't report a torque limit active value 4 on shift, but I do have torque reduction on shift from the TCU. Hopefully @jyamona can't provide a logical explanation.
Checked through my logs and toque limiters do appear sometimes on shifts but don’t seem to coincide with boost being 1.28bar or higher
He's talking about increased boost ceiling, not actual boost. It's a completely separate problem specific to DCT on any rom (N54 at least). No one runs over 1.28 bar/7FFF hex ceiling on DCT because it's a known issue.
Raising ceiling causes cuts to just about everything at once for an extended time on full request shifts. Not really clear, but imagine limiter 4 on it is likely in response to the condition, not the cause. Normal limiter 4 that everyone probably really means, you wouldn't even know existed without specifically logging it, but can be eliminated with DME tuning, as said.
Raising ceiling causes cuts to just about everything at once for an extended time on full request shifts. Not really clear, but imagine limiter 4 on it is likely in response to the condition, not the cause. Normal limiter 4 that everyone probably really means, you wouldn't even know existed without specifically logging it, but can be eliminated with DME tuning, as said.
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