93 XJS 4.0 Auto Conv.= * Shifts Hard ! * Only from 1st to 2nd ?? I've dropped the Trans Pan / Replaced Trans Filter / Trans Fluid... Solutions Welcome ! Thanks!!!

 

Um, a ZF 4HP24 electronic transmission I reckon.

Disconnect the battery, have a few beers, reconnect, and do the radio code etc, and see if anything changes.

Sometimes that will "de-memory" the trans ECU, and all will be sweet.

I am not real sure where the ZF gets its signals from to do what it does, but the TPS would be a prime signal, and it may be getting tired, or it is out of range.

Others more familiar will chime in when the time zones align a tad better.

 

I was having the same sort of 1st-2nd hard up-shift as well, on my 92 XJS 4L auto. However, it seems to disappear once the car has been driven and the fluid (obviously) has come up in temperature.
So I have not done any of your tranny work.
Let sleeping cats lie, I guess ?