factory test mode randomly enabling on tbi

hi guys... Have a issue on my 89 chevy pickup. Today on my way to work my ecu seems to have gone into limp mode. pegged the wideband at 10 and ran very bad... managed to get to work and did a reset on the ecu and still no good... happen to carry another with me so plugged that in with the same chip and still same problem... also happen to carry my pc with me so plugged in the cords and opened tunner pro to see what was up and it says it connects but not getting real data.. all error codes red... swapped between the 2 ecu's multiple times and finally it went back to normal... so scan was now working and i was watching it run and noticed that the factory test mode and diagnostic mode would enable for a moment then switch back to disabled... very weird.. I would suspect a short in the wireing harness.. any ideas???

Sounds like a harness problem. Check for a bad connection causing poor power or a bad ground first. Those trucks have grounds connections on the intake that tend to go bad and cause all kinds of ill operating.

Well i made i home... smoke was comming out from dash all the way!!!... i had the glove box apart so i can switch ecu easily however i cant seem to find what is burning... dont seem to smell like much either... not like wires burning... i ran pig rich all the way and it still runs even if there no chip in the ecu...lol...must be a short somewhere

Since i dont find anything burnt nor did the smoke smell like burning wires i think it was more from the heater core...rpms had to be high to get the truck to move so maybe the water was hotter then usual although the gage didnt show any hotter then normal...so now im pulling each wire out of the connecter to ecm and closing them up a bit with some pliers for a tighter fit... ive swapped ecms a lot so maybe they losened up and then ill go and recheck and clean all grounds

so far so good... went for a 20 min test drive and no problems