car only start with gas pedal on,runs bad stalls,always ran good before,changed

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the magnet behind front pully of crank-shaft,no change,getting gas,runs real rough,thinking maybe water in gas?tryed to get codes,would not read them?put a new heater core,a couple days before the car stoped running,thinking maybe the technition may have unpluged something?was thinking maybe fuel-filter?or injecters,need help?wifes car help,help before its to late??thanks