Shortly after replacing the gas tank, sending unit, and fuel pump on my 1997 Lesabre, I started getting a "bumping" sound from the tank expanding. Lots of pressure escaping when refilling. I replaced the gas cap as that is the most common reason. But it still throws the code. I have checked that it is sucking form the switch over the valve cover and have tried to seal off any vacuum leaks. Any suggestions for a cure? Thanks, Ron