Have you checked the connections and pins on the ECU? I've found that if the car has sat for a while then the connections will corrode and cause resistance issues with the ECU. If the pins and connections are determined to be clean and good then I would try to swap a known good ECU to try out. I don't know of any diagnostic you could try to verify if the current ECU is defective. The only test I know of is for the faulty FI relay ground with a bypass wire.