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Looks like around 4000 RPM in 5th you downshift to 4th, and then the transmission goes nuts.

Are you able to log the SST temperature via EvoScan or something similar? You can even use the Torque app with a Bluetooth adapter, you just need the right PID set up.

That way you can see if the fluid is really overheating, or if the overheat message is being caused by something else.

Does it happen when you downshift from another gear, say 3rd to 2nd, or 4th to 3rd?

Check the DTC codes in the car, you'll need a MUTIII tool for it since the SST codes aren't your "normal" codes; not sure if Evoscan 2.8 can do it, but back when I was having transmission issues the codes never showed up for me via Torque, even though the Mitsu techs could read them.

I want to say as an uneducated guess that you're losing complete fluid pressure when you downshift there and the transmission has no idea how to handle it, and shifts you into first gear. Last time I got the slowdown on a track, it put the car in limp mode but I don't remember it shifting be back into first gear. It could be an issue with the mechatronic unit perhaps?
 

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Looks like around 4000 RPM in 5th you downshift to 4th, and then the transmission goes nuts.

Are you able to log the SST temperature via EvoScan or something similar? You can even use the Torque app with a Bluetooth adapter, you just need the right PID set up.

That way you can see if the fluid is really overheating, or if the overheat message is being caused by something else.

Does it happen when you downshift from another gear, say 3rd to 2nd, or 4th to 3rd?

Check the DTC codes in the car, you'll need a MUTIII tool for it since the SST codes aren't your "normal" codes; not sure if Evoscan 2.8 can do it, but back when I was having transmission issues the codes never showed up for me via Torque, even though the Mitsu techs could read them.

I want to say as an uneducated guess that you're losing complete fluid pressure when you downshift there and the transmission has no idea how to handle it, and shifts you into first gear. Last time I got the slowdown on a track, it put the car in limp mode but I don't remember it shifting be back into first gear. It could be an issue with the mechatronic unit perhaps?
Looks like around 4000 RPM in 5th you downshift to 4th, and then the transmission goes nuts.

R:Yes, yes, the problem is more frequent when changing from 5 to 4 at 4000rm up to 4500rpm


The technician measured the temperature the 140 to 160 KM, is in the average of 102 to 108 degrees, maximum 110 (180KMH)
The overheating gave at 108 degrees

Does it happen when you downshift from another gear, say 3rd to 2nd, or 4th to 3rd?
R:
no, never, it's always 5 for 4, once it happened from 5 to 6, but the RPM was low, let's say, I should go back to 4, but I went to 6, then gave overheating

Do not generate error code, nothing appears on the computer

I forgot, mechatronic unit was replaced by a good one used, the problem remained the same


So, oddly enough, it seems that the problem happens more with low rpm

If I go back from 5 to 4, for example, at 5500rpm the problem does not happen
 

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Looks like around 4000 RPM in 5th you downshift to 4th, and then the transmission goes nuts.

R:Yes, yes, the problem is more frequent when changing from 5 to 4 at 4000rm up to 4500rpm


The technician measured the temperature the 140 to 160 KM, is in the average of 102 to 108 degrees, maximum 110 (180KMH)
The overheating gave at 108 degrees

Does it happen when you downshift from another gear, say 3rd to 2nd, or 4th to 3rd?
R:
no, never, it's always 5 for 4, once it happened from 5 to 6, but the RPM was low, let's say, I should go back to 4, but I went to 6, then gave overheating

Do not generate error code, nothing appears on the computer

I forgot, mechatronic unit was replaced by a good one used, the problem remained the same


So, oddly enough, it seems that the problem happens more with low rpm

If I go back from 5 to 4, for example, at 5500rpm the problem does not happen
Do you have a way to log this yourself? Either via a computer with a Tactrix cable or bluetooth adapter with Torque or similar?

102-108 degrees C seems really high to me outside of HPDE, hard driving or really bad traffic in hot weather, especially if you have decent airflow through the SST cooler (For comparison at 140 KM/H my SST holds up around 80-85). I went into limp mode at 125C on track, 15-16 minutes into a session.

If you can log it yourself, you can check what the temperature and clutch pressure for both sides of the clutch are during the downshift when this happens. From that you'll have better data to diagnose. I don't want to make assumptions with my baby tier knowledge, but if you're running this hot and your clutch slips during downshift (which I believe it will so it can auto rev-match), maybe the temperature is rising quickly and it kicks into limp mode?

I'd hit up Kozmic Motorsports over email. I don't know if they can offer remote diagnostics help for a fee but you'll be hard pressed to find anybody with more knowledge of this gearbox around.

Edit:
https://www.evolutionm.net/forums/evo-x-engine-management-tuning-forums/574170-logging-sst-useful-parameters-3.html
https://www.evoxforums.com/forums/showthread.php?t=53524

These might help setting up Evoscan to log correctly for you.
 
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