Alright m,y car got a rebuilt engine in and it runs fine. before i blew the motor *overheated at red rock* i was at least getting 14mpg. now the car wont even get 10mpg. and i used to beat on it alot worse than i do now. so my question is does the ECU need to be tuned? its a completly stock car except for a koyo radiator.

 

If you are running the stock ECU, there is nothing to tune (ECU wise that is).

 

Your ECU needs a good working o2 sensor for proper fuel economy. Also ensuring your air filter is clean and your sensors (MAP, TPS) are working/calibrated properly can help.