I wanted to be able to perform an injector balance test or fire an injector when the fuel rail was pulled to check spray pattern. For $40 you can buy a box that will pulse an individual injector after connecting to it. I found I could acheive the same thing just by charging a 10,000 uF cap by the car battery and then connecting cap to injector.
It would have been interesting to try this when I had mine fuel rail pulled and saw some brown crap build up at injector nozzel, just to see how it sprayed. A web search led you to write ups on injector balance test.

Perry
Hope this help somebody.