One exception: the wiring. Essentially, what you have is a hard-wired OR connection (low side drive). What that means is that The ECM pulls on the injectors, then lets go. The TFI is watching What the ECM is doing and, via various complex algorithms, also begins to pull on the same lines. The ECM lets go of the lines and the TFI continues to pull on them for a bit longer (keeping the injectors on). It's more complicated than that (I've read the patents), but that is essentially what is happening.
Now, you can disconnect the TFI power and the ECM is still able to yank on the injector lines, as normal. The TFI will simply not extend the injector 'on' time, because it is not active (powered). The TFI control will be out of the circuit, but the lines that are shared are still in there. A bad crimp on a connector pin will remain intermittent. Hey, it happens to the best of products, even TFIs...rare, but it can happen. Broken wires, inside insulation, can also be irritating. This generally happens on injector wiring, in the neighborhood of the injectors, due to incorrect or insufficient service loops (the wires repeatedly bend/kink due to sharp bends or tight stretches).
Good luck,
Rich P