Good compa, I think I know what your problem is.
First what we need to know, since accounts that your mechanic is not very experienced, is whether the fuel pump is connected to the original wiring, and I explain: in many cases, the fuel pump and the ignition signal of the air flow sensor are shared and come or from two relaxations connected to each other, or the so -called Ignition relay. In my particular case, cars have reached the workshop that after being badly diagnosed and having replaced the gasoline pump without need, these "hands" cut the positive cable of the pump and stick a direct one from the ignition. For which they solve the theme of the pump but not the rest.If that was the case, the normal procedure would be to achieve the electrical scheme and repair the damage.