i got an '87 tII and i want to change the motor to a '88 to '91 motor and i was woundering what the differences in the computer and if i need to change it and the wire harness and the computer

 

This should really be in the 2nd gen forum, but I can answer it:
To use the 89-91 ECU you'll need ALL of the 89-91 sensors, etc., and you'll have to do alot of rewiring to make it work. My friend did something similar, but with a non-turbo motor. If you want to use your ECU you'll need to swap the front covers to run the mechanical oil metering pump. You'll also need to put your injectors, sensors, etc. on the 89-91 motor.

 

By the way, 87 and 88 are about the same. 89-91 is different. Make sure to use the 89-91 flywheel with the 89-91 motor. Otherwise you'll have balancing issues.