As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
RIGHT AFTER ENGINE START AND THE START OF TAXI, BOTH THE COCKPIT AND CABIN FILLED WITH VERY ACRID SMELLING SMOKE. STARTED TO CLEAR UP ON RETURN TO THE GATE. PERFORMED TASK 21-00-01-100-801, OIL CONTAMINATION REMOVAL FROM AIR CONDITIONING AND PNEUMATICS SYSTEMS. ALL SYSTEM CLEARED, NO SMELL OF OIL CONTAMINATION FOUND.