I have a 71 Chevelle that I am tuning that has a LSA and a 4l80. The harness that was originally used for the swap was for a 6l90, but then they decided to go with a 4l80 and got a conversion harness from DSX Tuning.

The issue that I am having now that it needs to be tuned, is that I am not getting any vehicle speed reading in the scanner, and because of that, the shifting/lockup are all over the place. The harness for the trans only has a plug for the rear speed sensor on the 4l80, and I am getting an output shaft rpm reading.

I am guessing that I am missing something in the cal, or the t42 doesn't have the correct OS in it to get everything to function properly.

Has anyone done a 6l90 to 4l80 swap like this? Is there speedo settings on the ECM side of things that need to be done to play nice with the 4l80? I'll post up a log and the tune when I get my laptop handy.

Thanks.