99 4L80e in 93 6.5

[Tommy9103]

So this past weekend I bought a 93 6.5 dually with a bad transmission (fluid pump went out). I have a 4l80e sitting in my garage out of a 99 vortec truck 2500 so figured what the heck and stabbed her in this morning. I put the diesel converter in it) and when I went for a test drive the trans felt solid as a rock but will not shift threw the gears in any way at all not automatically nor manually. Any guidance would be greatly appreciated. Thank you.

[trbankii]

What was in the ’93 before - another 4L80E?

[Tommy9103]

Yes it had a 4l80e to begin with.

[trbankii]

I’m guessing that the ’93 is mechanical injection, in which case the control of the 4L80E was a separate computer from the ECM. I think that after going to EFI, the control of the 4L80E was all integrated. I’m not sure if that makes a difference between the two.

[DmaxMaverick]

Simply put, 93 and 99 model year 4L80E transmissions are not compatible, in either direction, without accommodation for the original technology.

[Tommy9103]

What would it take to accommodate?

[trbankii]

Simply put, 93 and 99 model year 4L80E transmissions are not compatible, in either direction, without accommodation for the original technology.

That’s sort of what I thought, but I wasn’t sure. So the standalone computer from the ’93 won’t run the ’99 trans and swapping all the electronics from the ’99 to make the trans run isn’t likely a viable solution.