83 Silverado fuel problem

Pickup died along highway, would start but not run. Has two gas tanks, one has a hole in it so have never put gas in it. Mechanic put gas in second tank and truck started immediately. He said it needed a new fuel pump and filter, which was installed. A few months later, exact same thing. This time I switch to “empty” tank and the fuel gauge shows almost full and the truck immediately starts. Call mechanic and he says if truck starts with second tank then fuel pump cannot possibly be the problem because there is only one. Huh? Exact opposite of first diagnosis. Truck has been snowed in since December, but now things are melting. Have to find a new mechanic, but need a clue first. What would prevent truck from starting with one tank and not the other? Thanks.

Unless I’m reading this wrong, it’s kind of obvious why it wouldn’t start when the fuel system is connected to the empty tank with the hole in it.

There must be something screwy with the selector valve (don’t know what it’s actually called).

If this engine is fuel injected, look for a problem in the switching of the fuel return. If the pump is drawing the fuel from one tank but the tank switch is sending the return fuel to the other tank, the other tank will eventually end up with all the fuel while the tank the pump is drawing from will be empty. Its possible that return fuel is going to both tanks while the pump is only drawing from one tank. Without specific knowledge of how the switching is done, I cannot see how it is happening but if the mechanic looks closely at the plumbing and design s/he should be able to figure what is wrong.

Hope that helps – let us know how this finally resolves.

Still clueless, but running. Just got the truck out of the shop and the mystery remains. Discovered that the bad tank is not connected to anything, no hoses, no wires, not even to the switch on the dashboard - and now the truck runs fine. No idea what the problem was, or where it went, but now that the mystery event has occurred twice, my carefree days of driving are now overshadowed by uncertainty. But I drive on!