[b3lha]

Originally Posted by svxistentialist

However I would expect the clock to be reading fast by a big percentage in this case. To make the clock [speedo] read correctly I imagine it would be necessary to give the TCU a new constant for multiplying out the speed.

I had a look at the dump of your UK TCU and it does have a similar constant for the speed calibration.

The same constant is used for VSS1 and VSS2. It's address is 0xC01A and the formula appears to be (940 x 1/ratio).

For a stock 3.700 it is set to 254.
For a 3.900 you would set it to 241.
For a 4.111 you would set it to 229.
For a 4.444 you would set it to 212.

That would correct the TCU's internal speed readings. I haven't been able to figure out whether it would also correct the speed signal that the TCU sends to the ECU and Speedo. But it wouldn't hurt anything to give it a try.

Note that the maximum value for this constant is limited to 255, so you couldn't run a 3.545 on this TCU without some extra work.