they need about 3 bar (maybe more been a while since ive read up on it) before they open so without a pump running the pressure will drop below that quickly, its firing and running albeit for a couple of seconds so i would say for now that theres not an air lock, thats also why you will see a pressure at the injectors and metering head, the only one that doesnt need high pressure is the blue cold start one but that only works when the engines cranking as an initial boost