On the fuel line, under the drivers seat on the frame.Take that 7mm plug out and drain it completely, maybe a half pint. Then take a can of throttle body cleaner, with the little red sprayer attached and clean it out. I use Q-tips to wipe it out after I spray it several times until it is clean again. It really gets nasty in there too. Replace the plug and you should be good to go. My truck had the same issues until a Ford mechanic told me how to fix it.