Looking for some help.

I have a 2013 LS3 that I have crammed into a 1947 chevy truck. I have installed a rebuilt 4L70e transmission to it. I have the original E38 ECM for the motor. I bought a wiring harness from Wiring Specialties who also took the original ECM and flashed it to run the 4L70e transmission. I bought a T42 TCM module online and had it reflashed and set to the LS3 vin number. The motor starts up and runs great. I can plug an HP Tuner laptop into the ECM and everything reads as it should. My issue is that there is no communication with the TCM. It does not even register in the HP Tuner. So, I have no speedometer and the transmission will not shift.

What or how should I go about getting the ECM and TCM to work together?

 

Harness issue

 

Brand new harness. The engine does see the neutral safety switch on the transmission and will start in park and neutral. The engine itself runs fine.

I've built street rods before but this is the first modernized with computers so I'm flying blind on this one. Pretty much learn as I go.

 

If nothing sees the transmission then its bad TCM (highly unlikely) or harness issue. Its a handmade new harness very easily could have an issue or installation issue.

 

I just found out last night that the company that made the new harness and flashed the original ECM did not change the operating system to work with a T42 TCM. I am searching for a local company that has the ability to reprogram the ECM as needed. I'm trying to stick with the original ECM and not buy a complete new system for both the ECM and TCM.

Thanks for your replies!

 

Sorry I assumed the ECM/TCM were programmed correctly, shouldn't assumed anything. We dont use a 2013 E38 with a T42, depending on if your trans is 13 pin or 15 pin we would use a 2008 or a 09-10 E38. On E38 the service number on ECM dictates everything you can do with them since the same service number covers more than one year sometimes. We sometimes use the newer service number that comes in the 09-10's also for better injector tables. Its also best to flash the E38 with SPS when changing the whole calibration since tuning software doesn't flash all the segments in a E38 like SPS does.