It's a 7.3L correct? I've seen many times and you need to replace ur fuel injector o' rings. The injectors have separate sections that get fuel pressure or high pressure oil. Those sections are sealed from each other to the cyl head where the galleys are for the fuel pressure to travel and high pressure oil to travel as well. Over time they get brittle and hard so the oring fails and the higher pressure oil will pressurize the lower pressure fuel area which pushes the oil into the fuel part of the injector and any unused fuel is then returned to the fuel tank where it's picked up pressurized by the pump then its sent threw the filter housing and into the fuel galley ports of the cyl head. So chances are ur tank is full of engine oil so check ur oil level too.