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:

* in the VE-table we increased the lowest-kPa row by +32, than gradually only +24, +16, +8, +4, +2... import VE table by saving [this vemscfg] to disk and dragging over the VemsTune VE table (VE tuning)

** this is just very approximate, to show the direction of changes, the engine must be fine-tuned for proper lambda 0.96 .. 1.00 at low load (that's why the wideband lambda sensor is installed)

* and in "Engine setup" dialog increase req_fuel slightly (eg from 3.0 to 3.1 msec)

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

See tutorial videos under [vems.hu/vt].