A quick n dirty option: If you temporarily set Injection mode to Multipoint group, you can then swap injection rate between 1 eng cycle and 1/2 eng cycle.  Lambda shouldnt change when you swap rate if deadtime is correct.  If lambda changes bump the deadtime either way and try again.  That will get it right at normal running battery voltage.  You can then do the same at a lower voltage by pulling the alternator fuse.  After you have a couple of points around normal running voltage you can c