TFI does not add resistance. That is not how it works. What it does, in a nutshell, is pull on the same lines as the ECM, that turns on the fuel injectors. The TFI sees when the ECM pulls on the lines, applies load-based algorithms and also pulls on the same lines. The ECM lets go of the lines, but the TFI keeps pulling on them for just a bit more, essentially adding fuel to your mix, then also lets go of the lines. All this is done in such a way that the ECM does not know it is happening, and is not stressed in any additional way.
What you will have is what is known essentially known as a hard-wired OR. It is a bit more complicated than that, but, you would have to understand their patent(s) for that info, and I leave it up to them to reveal beyond what I have.
All this is to say that your indy does not understand the operating principle, and does not need to worry on your behalf.
Enjoy,
Rich P
