Cranks but won't Start

I have a 2008 X5 3.O. The problem I am having is the SUV will crank but not start (This is an intermitted problem). Sometime it will start right up and sometime it will not. I was told that there is a 2nd fuel pump in the gas tank to push gas from one side to the other (This gas tank, I am told, has a hump in it and this fuel pump pushes the gas over it). If this pump is going bad and not working at times it will be obvious when the gas tank is below half a tank. I was told to keep the gas tank above 1/2 tank and see if the problem continues or stops. Please Advise!!!