The best way is to scope the ignition, but the resistor connectors are so problematic on 104 Waste Spark ignition systems that one just changes them with a plug change, just to save a lot of time. Along with using Bosch F8DC4 plugs... they don't like plats and don't need resstor plugs cuz the resistance is already in the connectors.. as SB states , each coil has to fire 2 plugs , in series.. even though the wasted spark [non compression stroke] requires less coil output demand . there is still a large gap for the coil to cross with the series circuit.
I have seen misfires codes on 104 HFMs , but the codes I referred to [21.22.23]
are actually coil output test codes , rather than actual Mis-fire... as stated , the early blue coils were known for low output and have been upgraded.