Another thing you can do to eliminate a possible problem is to fashion a test light in the power harness on the hot wire to the pump. If the light is on, you know your pump has power, light goes off, you know the pump is not getting power. If your pump is losing power, could be a bad relay, bad ground, OEM harness issue, or, a combination of the above.
Where did you connect your fuel line? Doe's your Fass system have teh filters? My friend hooked his fuel line to stock fuel system instead of the pump. He had 18 psi for a little bit then it would drop to zero he also had the edge juice with attitude for the guage. When I put the fuel line straight to the pump and put in a tee for the fuel psi sensor it worked great 18 psi all of the time.
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