EGR does not help MPG, it is strictly there for emissions. It actually lowers MPG and is the reason manufacturers are going away from it.
On a gasoline engine this isn’t true, EGR helps with milage due to the reduction in pumping work and it moves the timing needed to make peak torque for any given speed/load. The engine bsfc will improve with modest amounts of EGR in the cruise range.
The vehicles that don’t have EGR now usually have variable cam timing on both the intake and exhaust, and they accomplish EGR by moving the cams in relation to each other.
