Admittedly I haven't hooked up a scope to watch the DPR current control signal, but I do believe it is a bona-fide old school current control. A duty cycle of sufficient frequency should do the same thing. At a high enough frequency, I think around 100Hz, the valve won't respond to the individual pulses. Or you could take a duty cycle output to an appropriate transistor or MOSFET to then get a straight current output to the DPR.
40mA sounds way too much considering the measurements I've made. I increased DPR current by 2mA from around 20mA to 22mA at WOT by maxing out the altitude sensor input and that was enough to richen AFR by almost one point.
I believe -50mA is the max negative current specification and I've measured around -40mA when in overrun and fuel cut is active.
Personally, I think there is very little to be gained by changing the fuel injection control system. There are various means available to reach a desired AFR, albeit by making global shifts irrespective of engine rpm. So a little chip tuning is in order to make rpm dependent adjustments.
And as people above have pointed out, there might not be much to gain from a crankfire ignition system, except to make tuning easier and to make rpm dependent spark timing changes rather than the global shift that moving the distributor makes. So it's possible that there is a little to be gained from improving the area under the curve.
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