[diesel_john]

i was just toying with a prototype injection signal measuring sensor yesterday, you might need to attenuate the signal a bit with a couple Meg pot so you don't over range your A to D.
Parts: 2 used GM knock sensors, one 1/4" FPT x 1/4" FPT pipe coupling.
Tools: a drill bit the size of my injection line, a 1/4" pipe tap, hack saw or dremel.
Procedure: drill a hole in the center of the coupling, thread the coupling deeper on both ends until the knock sensors will reach in to the hole, cut one side of the coupling out until it will fit over the injection line.
Place coupling on a straight section of the injector line.
Hand tighten the knock sensors until they clamp on the injection. Wire the sensors in parallel. Attenuate signal as needed. see pic
i tapped on the bolt with a pencil and it made the analog bar on my Fluke jump, i don't think signal strength is going to be a problem.
Oh, BTW, there are two of these knock sensors threaded into the bottom of the water jacket on most injected 350 chevy's. make provisions to handle the antifreeze when you unscrew them.