heres the deal my 2000 powerstroke was running fine then i shut it off. got back in to start it to leave the house and it just kept cranking and cranking. finally i held the gas pedal to the floor and it started up idle for a minute and died.istarted it over and over and it kept doing same thing starting up idle then 20 seconds later die like i turned ignition off. fuel pump working and getting feul in the fuel bowl. so i waited over nite and went to start next mornig and started right up and ran fine all day till later that nite when on my way home and it died again and know it doing the same thing it did before. what could be my problem? Any help please