My fuel pumps leak the fuel back, it is possible a no return valve not working, it is the same for both pumps. Does someone have a chematic drawing to share so I can see how they work ? I do not like to open the pumps without know what is inside. I belive it must be a kind of flapper valve there as check valve. Since I have original pumps,and they have been fully overhauled in UK. I hope to have them installed, if not there will be Facet pumps in the car.