As Andy said. Wide Open Throttle. When the WOT switch is tripped, even with just key-on, all the injectors should burst once. You should be able to hear the injectors, but you could also use a NOID light plugged into an injector connector. A noid light is just an special LED substitute for the injector.
Also… forgot to ask… are you 100% sure you have +12V power at all the injectors with key-on? (The ECU controls them by providing an on/off ground). Ultimately all that power dumps out through the ECU to ground G6 at the rear of the car.
I made this for those needing to check the harness side pinout of the ECU while leaning over the rear bumper…
Paul K