What I believe is happening is these Pumps do "Suck" when running, have to say back in the day when I changed Pumps , cars were nearly all over Half full, I feel when your Pump is running it is on full pressure, Easy check hear....Remove the pipe on the 5th injector, place in a large Safe container as I recon your see full pressure, then unplug the Pump relay, with a short wire Bridge out Terminal "30".. with Terminal "87". the wire colurs your bridgeing.... "Red"...&....Red/black..tracer..... Pump will run now all the Time..i feel it will fill the container, Peter