If the ECU is detecting misfire at cylinder #2, this could be a result of an ignition problem as others have said. The way to know for sure is to replace the spark plug AND THE COIL at cylinder #2.

Additionally, it could be a result of a fueling issue at that cylinder, or any of a list of other reasons.

And as BOBB said, your ECU failures could certainly be the result of a grounding problem. The primary ground by the battery is one to check certainly, but there are many other grounds throughout the wiring harness which are critical to the proper operation of the vehicle and the health of its various electronic components. All of these grounds should be disconnected, cleaned, and refit to ensure proper grounding at each point. Even a properly connected ground can develop oxidation that leads to ground lift and thus problems that are VERY difficult to diagnose.

The "grounding mod" that many here have ridiculed as hogwash is quite effective in older vehicles for this very reason.