If you hear fuel pump running but only a little bit of fuel comes out at Schrader Valve and engine only runs for a few seconds then it is one of two things.
Fuel Pressure is maintained at the fuel rail by the Check Valve on the fuel pump and the Fuel Pressure Regulator(FPR) on the fuel rail.
Check Valve is part of the Fuel Pump, fuel can flow out but not back in, like a back flow preventer, this holds pressure in that end of the fuel system.
FPR is on the fuel rail, it is connected to the Fuel Return line, it is vacuum operated, you can check it's vacuum hose for gasoline, that would mean diaphragm is leaking, but other than that there is not much to test.
You can loosen the return line and turn the key on and off several times to see if fuel is flowing directly back to the tank, some fuel should come out but not alot.
Fuel rail/Schrader valve should have 35psi of pressure so fuel should squirt 20-30ft when you press it, just like 30psi of tire pressure, a little bit means no pressure