[Русский шпион]

Hi guys.
I have Z4 sdrive35is DCT transmission with JB4.
When I go WOT on speed about 60 miles/hr the car shifts back to 4th, sometimes 3rd gear and when it just starts to pull ( the gears are fully engaged already), suddenly a boost swings occurs , one or two waves 10-18 PSI, car stalls for the moment, then pulls normally with 16 PSI of boost, and upshifts without a problem.
It happens in all JB4 maps, except map 0 (OEM map 8 PSI boost max).
It happens with all driving settings , like sport and sport + with traction off...or just traction off..
It happens when I downshift it manually and then slam my accelerator...
It does not happen if I accelerate, but do not go WOT.
It does not happen when I go WOT on a 1 gear and car does not have to downshift.
So question is... what is it and how it can be fixed?
Custom tune of JB4?
If it is a "traction control" intervention how can I turn it off completely?
Maybe it needs a transmission reprogrammation/tuning to help it handle more powerful engine by not shifting down to 3rd gear from 7th?
��

[Terry @ BMS]

Add a JB4 log of the issue and we can look at it, but DCT power on downshifts are always a problem, as the DME is programmed for major boost reduction there to keep engagement smooth.

[Русский шпион]

This is what I was thinking myself, it is a DME action to adjust power level for the circumstances..I would like to upgrade my turbos to stage 2 (up to 25 PSI) but if I do it the boost swings might be dangerously high on downshifts.
Can I suggest to make an update for JB4 that will enable it to take over the control of DME for this action?
Other suggestion - optional for JB4 complete traction control off.
In any case my car will go in winter hibernation this week - optional for Canada . So I will make a log of the problem sometime next year when it will wake up for the summer fun.

[Русский шпион]

M3/M4 cars have exactly same models of DCT and up to 18 PSI boost level. I guess their DME and/or transmission computers are adjusted for the power/torque surge on downshifting.
If you need a test car - I am all yours. I can remove my JB4, send it to you for reprogramming and test the results on my car . My Z will sleep in a garage till May 2018 anyway.

[Terry @ BMS]

The first step is to capture a JB4 log of what you're feeling so we can base any changes on actual data.

[Русский шпион]

OK, will do ASAP. If you will not hear from me in a next two weeks - means I will be able to catch the log next year only.
Thank you Terry.

[Русский шпион]

Hi Terry. Was able to make some pulls today with logs in a different settings (normal traction off, sport, sport+).
One log is on map4 just as a stock comparison .
Others are map 5.
Maps1 and 2 and 6(factory preset values) all do the same thing.
I will be out for a week in a vacation, so would be out of reach.
Thank you for looking.

[zr666zr]

Привет, Нашлось решение проблем?

[Ke93]

Originally Posted by Русский шпион

Hi guys.
I have Z4 sdrive35is DCT transmission with JB4.
When I go WOT on speed about 60 miles/hr the car shifts back to 4th, sometimes 3rd gear and when it just starts to pull ( the gears are fully engaged already), suddenly a boost swings occurs , one or two waves 10-18 PSI, car stalls for the moment, then pulls normally with 16 PSI of boost, and upshifts without a problem.
It happens in all JB4 maps, except map 0 (OEM map 8 PSI boost max).
It happens with all driving settings , like sport and sport + with traction off...or just traction off..
It happens when I downshift it manually and then slam my accelerator...
It does not happen if I accelerate, but do not go WOT.
It does not happen when I go WOT on a 1 gear and car does not have to downshift.
So question is... what is it and how it can be fixed?
Custom tune of JB4?
If it is a "traction control" intervention how can I turn it off completely?
Maybe it needs a transmission reprogrammation/tuning to help it handle more powerful engine by not shifting down to 3rd gear from 7th?
��

to my knowledge this is caused by a button on the bottom of your pedal that puts your car in an optimal gear for performance mode. id imagine this setting can be tweaked like the jb4 has the ability to disable this function.