I just tested this with the guino. At first, it was reading GPH according to engine speed (like before). I went and messed with the Inj delay us, and with it set to 0, the guino would register more GPH if I had the A/C on than if I had no load on the engine.
However, even with the injector delay set to 0, the reading would still change according to engine speed (a lot). This leads me to believe that the time of the "peak" is constant, regardless of RPM. I think I need something like a capacitor that would "hold" the voltage up. The "peak" would charge it, and the pulses from the "hold" would hold it up, but when the injector stops, a resistor drains the capacitor. Like this:
I just don't know what size capacitor I need.