Re: 2004 jeep grand cherokee 4.0
If you want to know if a leak in the evap line is causing the problem, you could easily plug the line under the hood. The purge solenoid is mounted on the left fender (seen from drivers position) and you could follow the lines to see which one is going to the engine inlet duct. You could plug that one temporarely to test. But you have some vacuum leak for sure if you hear a hissing noise at the rear, so you better just try to solve that and be done.
Never touched the fuel lines, but as far as i know will the fuel pump run constantly when the engine runs and will the fuel pressure regulator in the filter assy regulate the fuel pressure to around 45 PSI (when im not wrong about the figure) and will the surplus fuel be send via the return line back to the tank.