Can removing the muffler hurt the motor a friend of mine at work has a 92 Ford diesel and it has 200,000 miles on it. Had it at the repair shop they told him he has 2 bad cylinders a bad injector and a valve is shot. His Dad says it is because he removed his muffler and there isn't any back pressure on the motor. I figure 200,000 in a Ford 7. 3 non-turbo is pretty good.