Mitsubishi Repair: stallin, mitsubishi cars, o2 sensors

Question
The car run's perfect for about 45 minutes at first of the day. Then I hear the ECM click and turn"s off the car like it was with the key. I pulled the key out for 10 or 20 seconds and it starts for a minute and does it again. would the o2 sensor be weak and makeing it tell the ECM to shut down the engine? My uncle that own"s the car said they had it happen last year and they replaced the  ECM and it worked till now. The ECM is in plain site and there is a little corrosion on the side of it. Could it be in it also? They also put a used one in it. If yes to replace o2 sencer or ECM , would auto zone or part stores carry these items

Answer
Billie,
Older Mitsubishi cars are known for troublesome ECMs.  You can read this article for more information:
http://www.90gsx.com/eclipse/cap/caps.htm

It's possible the ECM you used as a replacement could have developed the same problem as the original.  I doubt this is an O2 sensor problem.  If your O2 sensor went bad, that should not cause your car to shut down; it would only lower your fuel economy.  Places like AutoZone do sell O2 sensors, but they normally do not carry ECMs.  
Good luck!