The old v3 was very non-standard.

Originally low voltage flyback.

~10 Ohm injectors so the replacement ECU has 30V flyback which is better. But you need to increase VE table especially at low kPA to get appr +500 usec longer pulsewidth.

Without tuning the VE table the engine can be lean, undrivable, and misfire. The USB-RS232 can indicate misfire by disconnecting.

solution: Increase fuel pulsewidth

You can get an idea of the direction of required changes:

Alternatively, in injector settings "injector opening" can be increased (eg. from 208 to 720 usec).

See tutorial videos under [].