Managed to get the winaldl software up and running perfectly trough usb FT232 adapter.
It provides a steady stream of data on all things when car (89 g20) is in ignition on, engine off.
However with engine running the datastream gets corrupted somehow, and values recorded takes on all sort of numbers.

On the usb adapter i can change from 5 to3,3 volts, but this didn't change the results.
So Im thinking it could be one or more of several things?

Bad ground somewhere. wiring harness
Bad alternator, or alternator ground?
Ignition coil, ground
Spark plug wires running to close to the main wiring harness causing interference.

Anyone has experience with this, suggestions would be appreciated :)

BR
/Alex