I have been fighting what I thought was a auto trans problem for 6 months until today. After several phone calls I finally found a guy with a scanner to read the TCU. He couldn't access the TCU or PCM, but could manually access the ECU and turn accessories on/off. The whole time he would constantly get a message saying No DTC's present. Does this mean I need to flash my ECU? The ECU is the standard black box from the factory.

I do have extra mods done to the car: 16g turbo, BBK throttle body, 6" cone aircleaner, high volume fuel pump, and a few others. At this rate should I just buy a new ECU and software? Or will the stock ECU still work? I'm a wrench monkey, but this electronic stuff is still a little mumbo-jumbo yet. Trying to learn one thing at a time, but need electronics to work in order to keep wrenching .

Any help is greatly appreciated. As an extra note: the car does run (beautifully), wideband is a little high (14.7) but hasn't ever been calibrated, and the only codes are for the catalytic converter (which is removed) and for the fuel pressure regulator (aftermarket installed). There are no leaks of any kind, anywhere. Just ask if you need more information. Thanks again for looking

Not quite sure why you think you have a bad ecu. No diagnostic trouble codes present is a good thing.
Don't forget every time you disconnect the battery you reset the ecu, and mitsus can take a long time for drive cycles to be completed, especially for emissions monitors.

Would that cause no communication between the ecu and tcu? I'm just really confused as to why the scanner couldn't connect with the tcu or pcm. There is an obvious problem with getting 12v from the main harness into the valve body. Battery is 12.25v with car off and 13.5v running. Harness to the valve body only carries 8.5v and I've tracked it to the tcu, but it can't be read.

Tried pulling codes off the tcu 3 times with 2 different multimeters, no go. Would pulse once then nothing. Thinking about pulling the tcu and looking inside. Is it the little black box under the radio? Looks like a 3" x 4" box that's between the ecu and shifter?