I don't know much about fuel injected cars, but your injectors could be fouled, the fuel pump could be shot, there's a lot of things that could happen.
Did it just all of a sudden drop in horsepower? Have you checked your spark plugs? A lot of the time one or two plugs can get so dirty it'll stop firing that cylinder.
Also, is the mechanic saying you need a new "fuel pump system" or a new "fuel system" cause a fuel pump is cheap as hell, a fuel system isn't. Ask them specifically what's wrong, make sure you don't get ripped off.
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