First off, 1989 is not an OBD 2 system.
Second Mitsubishi did not support flash programming till the early 2000s in some models, later in others. That is a vague statement but I did not feel like looking up the details.
But basically non Canbus ECUs are generally non flash.

Flash programming is where we can reprogram the lookup tables such as mixture and timing in the computers.

Cheers, Charlie
If It ain't broke, Modify it!
87 Montero turbo Converted back in Spring1989
95 Montero SR 3.8 DOHC Only one?
93 Pajero 3 door 6G75 Mivec with paddle shifted 5 speed
Then a Gen2 SR with full coil independent suspension.