An LM331 voltage to frequency converter could be used for the injector signal. It would take a bit of a rewrite to measure the frequency instead of pulse width but nothing bad hopefully.
Another possible option for dc use would be use a
voltage to pwm circuit to feed the injector signal as is. The shunt resistor would have to have a filtering circuit to give a smooth signal to the converter circuit.
That is about all I can think of right off for using it as an ev monitor
