The fuel pump went out on my sons 2004 GP GT. Replaced the pump and when I started it up I noticed through the access panel in the trunk the plastic gas tank started to collapse and the top of the fuel pump sank down about 3 inches. I removed the gas cap and it sucked a large amount of air into the tank and the top of the fuel tank returned to its original position. I put the gas cap back on and the tank started to pull a vacuum again. It has not thrown a CEL code. Could the solenoid valve to the intake manifold from the EVAP system be stuck open? Also thinking this might be what killed the original fuel pump. If anyone can help give me some direction where to go with this I would greatly appreciate the help.
