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      03-27-2024, 11:49 PM   #11
SayedNaimi
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Drives: BMW 4 Series 430i
Join Date: Aug 2023
Location: Luton, United Kingdom

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Quote:
Originally Posted by cyam View Post
So I had a similar although much more minor version of this issue.

As it changed gear at WOT from 3rd to 4th I would get a shudder. And as it hit redline before that gear change, it seemed like it was hitting the rev limiter and bouncing around first, then change with a shudder.

So I found out it was my tune that was the issue. The tune was fudging the torque values being sent to the TCU. Instead of reporting (e.g.) 600nm to the TCU, it was down-scaling them and just saying "500nm" - because the gearbox has torque limits at around 550nm. So the tuner, to avoid limiting the tune to 550nm, simply got the DME to lie to the TCU about the actual torque being sent.

So this prevents the gearbox sending a torque reduction request to the DME.

Problem is that the gearbox thinks its only getting 500nm and adjusts line pressures etc for 500nm, but it was getting 600nm. So it starts to cause the gearbox to slip, shudder etc.

When I figured all this out, I ditched my tune and switched to MHD - which does not do this, and my gearbox has not had this issue at all since.

That's what happened to me. Your tune may not be doing this and its something else entirely. But maybe this can point you in the right direction.

To me it sounds like the gearbox is not using enough line pressure for the torque its been sent. Could this be a possibility?

Also remember that the gearbox does reduce torque at the gear-change to smooth out the change and reduce wear. There are one of three ways it can ask the DME to do this. Could it be that the torque reduction at gear change settings are causing issues?

I am no expert but hopefully this helps in some way.

Thing is my M340i has not been tuned at all. I have been pulling my hair out trying to solve this for the past few months and there is nothing I can find. Ive taken to BMW and a gearbox specialist and they also have no idea.
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