there are other tricks.
not tried by me but will work , (and can set DTC's or not) (had this fail on many cars)
Kill power to Distributor ( dtc , cmp.failed 42 Dtc but autoclears,CEL)
or
kill power to spark feed back line ( my trick) this will set dtc only in memory and is erased as soon as corrected. ( i think)
this is called the Ignition suppressor on Suz. cars . (not on XFI , sorry)
it is used for the Tacho signal.
so open the techo line and ECU thinks , dead spark, can cuts fuel immediately
the DTC is 41 (loss of spark)
spark feed back is (on my suz)
brown at supressor module
and yel/blue at ecu.
Some DTC only store while ECU has main power.
this is one.
now i will fetch your schem.
this may prove the best solution.
on suzuki's
know your model car first before hacking , they are all diff
your exact schematic is here. get it. XFI
http://kick-fix.com/look/metro/