Hi.
In
purely mechanical pumps, it should be possible, in my opinion, to initiate the start of pumping (and thus the start of injection) by using the traditional method of twisting the pump.
Unfortunately, there's no injection pressure adjustment voltage that would indicate the "success" of the action. That is, you have to measure the stroke of the injection plunger using a special device, as was the custom among old-school mechanics.
For the throttling behavior, there might be adjustments available, possibly but perhaps inside the pump

.