why does my new fuel show 50lbs pressure then after i tried starting it i can only get 20lbs pressure ive done all my checks for the power and relay i have 12v and relay is working
O-ring or seal may have slipped off or misaligned during install, fuel pickup dirty or corroded/broken section of tubing may be sucking air instead of fuel. If you have all power to fuel pump and are checking fuel pressure during cranking then it's down to the fuel pump not working properly. 50PSI is also the minimum needed and you say it drops from that after initial power on, I'd recheck all your connections/orings/filter element etc.
This post might help you: http://www.batauto.com/threads/98-chevrolet-k2500-fuel-pump-inop-low-pressure-5-7l-engine.9959/
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