When i've had to check fuel pump ops over the years in 240's I never even used a pressure gage (same pump set up on 900). I removed flex hose from fuel rail and secured it in a gallon jug (be careful, fire!!) and jump out both pumps to run, then jump one or the other to run and observe outputs. The tank pump by itself if working properly with good fuel level and with no line problems will be able to pump through a static main pump and deliver a steady low stream of fuel at 4-5 psi, with the main pump you will get a vastly increased stream at 30-40 psi. Now again becareful not to spay gas every where, or in your face! I have ID both pump problems over the years this way and it works, just don't burn yourself up doing it!