The INJ fuse powers only the coils. I know, it doesn't seem intuitive, it made me look a couple of times. When the powertrain relay energizes, it applies power to the coils, engine running or not. If the coils or the circuit is shorted to ground, it will blow it as soon and the relay is engaged. The two diagrams I've posted are basically all there is to that circuit. The coils receive power and then also receive a separate signal to fire the spark plug.I’ve been following this trying to absorb knowledge for when my time comes and this fuse problem is a good puzzle. I don’t have a donor or wiring diagram, but I have a question that I hope helps. What does the INJ fuse power? Coil packs only doesn’t seem like the circuit would be named INJ. Only turning the ignition on without trying to start also doesn’t make sense for the fuse to blow. Are the injectors powered by that circuit or a fuel pump? They would get power with just key on. Maybe a short in that part of the circuit.