dcb,
if you get a chance with a scope, this just might work to test an injector. chan 1 & trigger hooked to injector voltage.
channel 2 connected to a 'knock' sensor or piezo-mic glued on top of the injector. (accelerometer)
what you should see is an acceleration when the injector pin starts to move and then when it hits wide open a larger acceleration spike.
Upon closing the largest spike will probably be when the pin snaps shut. Don't be surprised if the pin bounces a couple of times when it hits the end stops. John