From my limited research into injector driving that portion actually occurs when the injector drive is removed to close the injector and is the result of the back-emf generated as the coil current collapses. The waveform is what one would expect for the voltage at the drain of a power MOSFET driving the injector in a 'peak-and-hold' mode. The injector opening pulse actually starts at about 1.8 mS (where the waveform drops close to 0), continues during the peak phase to ~ 4.4 mS, then becomes a rapidly-oscillating PWM wave which reduces the coil current during the hold phase which ends at ~7.8 mS. The slight hump in the waveform between 8.6 and 9 mS is a result of the valve pintle closing. So the injector open time starts shortly (say 0.5mS) after 1.8 mS and ends at ~ 8.6 mS (i.e. open time = 6.3mS).I've also done some preliminary analysis on the pulse that the injectors receive and have attached an example. The portion that is of interest is close to the 8th horizontal division which goes from 15v to about 45v peak.
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