T43: 2007 Escalade (2) Roms: 22" Rom and 18" Rom Calibration Speedo Adjustment

[raceghost]

Hi all,

New to the GM tuning, and have posted in the E38 Section a couple of times.

Purchased Truck used, blown motor, transmission, and rebuilt it all. Interesting had some issue with TCM and transmission acting up. Was suggested I check programming. TCM was flashed by GM Dealer upon NEW Transmission being put in. I went to a friend who has access to all the GM ROMS via official GM programming access. We found some things interesting. My Cadillac is the Luxury Version and came with the 22" Rim upgrade. When we hooked up to the programmer, we found (2) different calibrations for rims sizes. Both Calibrations are numbered and registered differently. Both of them have notes for 18" version, and 22" version respectively. I have attached them below. So the calibration on my truck was the 18" version, and reading all the nasty details, and GM warning labels on their ROM Flash site, it states, do not program TCM with wrong RIM size Calibration. We promptly updated it to the 22" TCM Version. I have used the EFI LIve to read both ROM's and versions, and done a comparison within the software to see the differences, they are subtle, and only in a couple of tables. But I digress, download them both, and do the compare for yourself. We also did a Shift Relearn or reset the adaptive data.

Note: If you have 18" rims and wish to go to 22"rims, then here is the latest updated ROMS for you. or visa versa, getting rid of 22" and going to 18". I did notice some subtle differences in transmission once I loaded the 22" version to my TCM.

My nest question, is Tire Size calculation.
I have attached a stock E38 Rom from my truck, as well as an updated rom for tire size and a couple of other things. Specifically, you need to check the Speedo Tables and relating tire size calculator tables. I think you will be horrified at what you find in the stock rom calibration on how the Speedo is calculated. You will see that the numbers in the stock rom are craxy, in fact, when you hit the tire calculator function, it tells you that the tire size is set fo 72" tires...lol. Check it out.

Either way, In the edited rom, you will see that I have it set for 285/45/22, specifically, the tires I have from Cooper say they are a 32" tire, not the calculated 32.10 that most tire calculators give you, this is directly from coopers website.
My issue is this. On the stock rom calculation, my spedo is about 4 MPH slow compared to GPS speeds. i.e., it says I am going 84 mph when I speedo and digital speed on the dash say 80. In the modified rom, with the 32" conversion, it is 3 mph off same way, GPS says 83, Speedo says 80~81.

Heres where it gets wacky, and I have tried multiple ways to close the gap to Speedo displayed=GPS to no avail. I have tried the 32 tires size with multiple adjustments to the "Speedo Fine Tune" table with in the EFI Live Speedo Calculator, where you plug in the Displayed speed and Actual Speed, no change. I have increased it 3 times by 2 miles per hour, each time it changes the "Pulses per mile" down by calculation, flash it back to the truck, with no change it is constantly 2 miles per hour off. I have even started over, set tire size to 32, 32.25, 32.5, 32.75, and 33, with no change either. Virtually I have played with all the tables within the first tab of the speedo parameters to no avail. I can't seem to close the gap below 2 mph variation, which makes no sense. i.e. stock rom to Speedo calculation adjustment for 32" tires closes the difference of 4mph down to 2 miles per hour, so one would think that increasing the tire size even more, would do the same thing...

So, then I got curious about what was in the same tables within the TCM. ON my older 05 Duramax, everyone stated never to do anything to the transmission with the TCM. I have read on the T43 to not do the same. But interesting is in the TCM programming, the speedo parameters are scaled for 30" tires. I am half convinced to run a test, and make the 32" adjustment to the TCM tables to reflect the same information that is in the E38 ECM tables. Mirror them if you will. Not touch any other tabs within the speedo parameters speedo calculator on both the TCM and ECM.

To clarify, what I am saying, is look at both my stock ECM and TCM files, and look within the speedo parameters, and click the speedo calculator, look at the first tab in both windows, and see the difference in how the ECM data looks to the TCM data within those tabs. Its like GM just completely hosed the handshake between the ECM calculations and TCM calculations...

Any help or thoughts would be greatly appreciated.

Thanks in advance