No, updating the computer system is optional, OBD2 may have it's ups, but it sure as hell has it's downs as well. 94-99 engines are all identical, EXCEPT, for the addition on one extra sensor on the plenum for 96-98, and then another addtion in 99. (96-98 has the pressure sensor, 99 has an addtional temp sensor as well.) basiaclly, just changing over the intake manifold will make any of those engines 100% identical to any other. if you wanted though, you could upgrade (or downgrade as the case may be) to OBD2, keep the 97 plenum, and just change over the wiring harness, and control module to work with it. (i am pretty sure that the 94-95 harness is complete, but is missing one section of the harness with that sensor plug. I determined this because when I looked at my computer, and had out my 97 manual, the wires designated as that sensor WERE located in the plug. so it seems that the addtion of OBD2 is just a matter of swapping or adding a harness or two and a computer. (pressure sensor, and OBD2 had a downpipe with 1 additional O2 sensor in it. what do you want to bet both those sensors are on one harness? Mitsubishi had a way of making the 3000GT have future changes, but just not have them active on a certain year.
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