Engine Exhaust System problems of the 2014 Ford Mustang

Upon accelration to pass a slow vehicle a strong odor started to fill the vehicle, almost like a propane smell. This I later learned to be exhaust fumes, or I should note, unburned fule passing throught he system. This is the 3rd time this has occurred, and only does this under acceleration when passing slower vehicles or using more power to ascend hills or mountain type roads. Vehicle throwns no ses codes. Vehicle does not stutter or hestitate, but as noted does produce a foul smell under harder acceleration.