I have the same ole dual tank problem like so many others: when the front tank is selected, the rear tank gets empty, too. Searching all the archives, it seems to either be the tank selector valve or the check valve on the front in-tank pump. How can I find out, which of the two options it is?

 

Put different amounts of gas in your tanks. Does the gauge show about right for each tank when you flip the tank selector switch? If so, then your selector is probably good. If you have a bad fuel pump check valve, one tank will pump into another and eventually overflow the tank. Very dangerous. On my truck the back tank would pump into the front and cause overflow in the front tank. When this happens the fuel pump check valve IN THE TANK THAT OVERFLOWS (accepts fuel from other tank) is bad. A replacement fuel pump costs about $165-$200. They aren't hard to change, though. Either drop the tank and change the pump or just take your six bed bolts/nuts off, unhook back lights, take tailgate off, loosen fuel filler hose clamps and have a buddy help you lift the bed off. This is much easier than dropping/reinstalling either tank, unless you have a lift handy.

 

That's what I feared :-( The switching between the tanks works fine (easy to see: one of the gauges always shows empty), but the rear tank gets empty while I'm on the front tank. I don't even dare to try to select the rear tank while the front tank is still full. Seems like the PITA check valve then, eh? S**t!