240 is messed up HELP

[kingkaylo51]

ok so replaced the injector fuel in oil right so figure the injector cused it i fixed the o ring in injector and drained the oil 2 and half gallons of mixed fuel /oil came out replaced it oil and engine is having a VERY hard time cranking then cranks fine then hard agian put wont start i have not takin anything off the car but the injector so far my friend was driving it when it just stoped running a huge cloude of white smoke out the back then died and haset started once if any one elce knows what is going on i need help before i buy a new motor or see if i can rebuild it