[mwebb]

lean signature shows up in the spark waveform
here

the sixth waveform shows a lesser lean condition than the others , this waveform is captured during DFCO so all injectors are shut off
all spark waveforms should show show lean condition by a consistent amount
that #6 injector is leaking
OR the purge valve is near #6 and the purge valve is open during the capture .

you can use the same ignition waveforms to show when a particular cylinder is
lean or rich
at cruise OR WOT
and it is very possible to have the fuel trim for the engine or bank at stoich when as many cylinders are lean as are rich
total trim is correct
trim per cylinder can be way off , and efficiency and FE suffer because of it

your particular engine will yield a great deal of information regarding fuel trim and internal pressure through the spark waveforms

on more advanced systems

you can graph KNOCK RETARD per cylinder , knowing that lean cylinders will tend to "ping" more than un lean cylinders , the cylinders that are knock retarded , are lean
OR have carbon deposits OR more likely
both