PERIODIC SMELL OF FUMES OR BURNING SMELL INSIDE THE CAR WHEN RUNNING. PRONOUNCED SMELL UPON HARD ACCELERATION AS FROM A STOP OR UPON MERGING ONTO HIGHWAY. HAS HAPPENED SINCE SHORTLY AFTER BUYING THIS AS A USED CAR LATE LAST YEAR. MY BOYFRIEND DRIVES THE VEHICLE A LOT AND THOUGHT IT WAS JUST OUTSIDE TRAFFIC SMELLS ENTERING THE CAR BUT AFTER USING THE A/C ON RECIRCULATION MODE, WE REALIZED IT IS COMING FROM OUR EXPLORER AND ESPECIALLY UPON HARD ACCELERATION.