First low cost quick repair...Install non-return valve at fuel pump location. You will need non-return valve, 1 1/2 ft of gas line hose, 2 suitable clamps. All compatible with sizing of fuel pump hose dimensions. If this does not work read my post on pulling injector rail, pressurize fuel line and put little pill vials under each injector and wait for 1 hour to see which injector may leak.