I have a test setup in the car. I used some clear hose going from a water bottle in the cup holder to the pump then to a vacuum port on the engine. I wired it to the injector with no resistor on the wire just to get a feel for the max flow of the pump.
I started the car and the motor just jumped back and forth. The inductive kick from the injector was high enough to keep it from doing anything. I found a random diode I had laying around and put it inline with the motor to get rid of the reverse current. I didn't have a meter or a wiring diagram with me so I have no idea yet if I have it wired in the right direction but at idle it was pumping a very tiny amount of water so it was good enough for a quick test.
I will get a meter and make sure the power is going the right way to the motor and the diode is facing the right way. Then I can dial in the system but it looks like it should be no problem to get it working very well.
So far the total parts list is that pump listed on the first post and a
25W 200 Ohm Round Ceramic Wirewound Potentiometer and a diode. The diode needs at least a half amp current capacity or so. I will leave it hooked up and drive to work tomorrow and see how much water it uses. Then I will put the variable resistor in and try and dial it in.
I would take a picture but right now it is just a ball of duct tape on my battery handle and a bit of hose so it doesn't look like much.