I have a 1998 ford windstar lx. i drove to a

i have a 1998 ford windstar lx. i drove to a friends house, then when i left the house 45 min later the van was running rough. whent down the road abit then the engine light came on, then about a minute later the engin light started flashing. the owners manuel said the the flashing engin light means that the van is misfireing. what could cos this problem. and i also fill up at the gas station before i went to my friends