why not use a vacuum signal, its quite better as it gives you more accurate data of engine load, use that and calculate the volumetric efficiency of the engine, size, manifold capacity and cam timing if equipped.
The system you are using is dead head - you will need to isolate it and find out the flow rate of the injectors at the given calibrated system pressure (usually between 45-50 psi). You can then use the exhaust AFR or O2 to countercheck your data - if you are getting full and properly phased burn.