I'm coming back around to a 100k trim pot in parallel with the zener for now, with optional capacitor for pwm based hold circuits. I do want to keep the emphasis on precision however, that is the main advantage the mpguino has over OBD solutions post 96.
I got a peek at an existing peak&hold circuit and not including connectors it had twice as many parts as the mpguino. Basically they combined every option we have discussed thus far, and it still needed trim pot adjustments and resistor swaps
So some guess at the pwm frequency is probably in order. The pwm in this, possibly unrelated to anything automotive,
graph has a period of 600uS. We are subtracting a 500uS "mechanical delay" from each pulse. So it is believable.
Unfortunately with a trim pot in the circuit it means the the target reactance of the capacitance also moves around, which means two trim pots for the subset of injectors that are both peak & hold AND where the hold circuit was implemented with PWM. I don't know how to guess at those numbers.