sooo... my 2000 F250 was down to getting about 6 MPG. I took it to the dealer and then ran it through the "tests". They told me #8 injector was bad and they replaced it. Heres my question.. will 1 bad injector cause a drop in fuel economy of 70 percent or more? SHould I believe they have found the problem or dig deeper?

Thanks ahead of time!