'94 Eagle Talon, 2.0,automatic, non-turbo
After owning this car for 2 days the engine went sour and I had 2 "mitsubishi techs" install a guaranteed junk yard engine with similar mileage (111,000). Ran fine for about a week then would not start but could hear the starter relay vibrating under the console. Tried a new relay and it was the same so I put the old one back in. Disconnected battery and then when reconnected it would start but the problem returned and the only way to start and run was to manually short the relay with a quarter. "Techs" said it was the ecu so I had it rebuilt. Put it in car started died a couple of times then ran great for about a 10 minute test drive. Tried it again and it ran for about 2 minutes and again will only start by manually grounding the relay. I'm thinking it is not the relay since it started and ran fine. I'm wondering if there is something that was done or not done when swiching the engine which is frying the ecu? Appreciate any thoughts. Thanks for your help.

Dave

The only way it could fail again would be if the rebuilt ECU had other problems with it. I would have those "techs" check the timing on the guaranteed jukyard engine that was installed. It may also have bad compression or problems with some of internals (valves, springs, pistons, etc..)

They should also check all the harnesses that are required to be connected when an engine is installed. There a couple dozen of them, and if any pulled out or are not connected propertly, that will lead to problems you're describing.
Good luck!