How are you going to connect the two lines? If nothing else, a fuel filter might work to just splice between. You'll need to connect the supply line from one tank to the supply line to the high pressure hose (I'm not sure the positions of the hoses). You'll also need to connect the return line from the fuel rail to the return line back to the tank that you have the supply line coming from. It's sounding like something other than that valve, have you tried pulling the codes?