Hi Gary,
I hesitate to argue too forcefully about the VP-44 because there are only a few thing that I know to be fact. The rest is an educated guess. Here is why I think what I do.
I know, for fact, that the VW TDI injector is what provides the pilot injection charge. It is done mechanically through the needle and springs, but the injectors definitely do that. There is no electronic control involved. Just mechanical parts. Of course we know that the Cummins does not have this type of injector... or they'd be much quieter.
I know, for fact, that the VP-44 is capable of some very fast fuel control. At full load, and at max RPM the fuel rack is capable of opening and closing the spill port fast enough to to deliver full throttle fueling to one cylinder and none to the next. Using most diagnostic scanners you can do a cylinder balance test at full throttle. The VP44 has one set of puming plungers(2), inside 1 rotor that do all the fuel delivery for the engine. That means the fuel solenoid can move the spill port from fully open to fully closed and back again between cylinder firings. That's fast!
Are you sure the solenoid you are talking about isn't the solenoid that controls the spill port? I don't believe it is mechanically possible to cap the plungers of a rotary pump without causing it to explode. I know that diesel fuel has some elasticity at injection pressures, but not that much!
It all would make sense if you're saying that at the end of a normal injection period the factory pcm commands the spill port open, stopping the injection event. The fueling box sees the injection event end and then closes the spill port again(allowing pressure to build in the injector line again) and causes a second injection event. I'd sure love to see that happen on ascope. Any chance anyone has some screen shots? or live close enough to me (near syracuse, NY)so I can get them myself? That'd certainly provide some answers quickly.
Joe