1996 GMC Jimmy

Engine Mechanical problem
1996 GMC Jimmy 6 cyl Two Wheel Drive 180000 miles

accarding to manuel the fuel line should have constiont presure. When I turn on the key. I have pressure at fuel filture. After I reconnect the fuel filture line.I check pressure at carburature and there was no pressure.I then cycle the key and there was pressure at the carburature but not enuff to start the car. The car will not start because of no fuel. When I pure fuel into the carburature the car start. Need help please.