As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ON TAXI OUT, GREY/WHITE SMOKE WAS NOTICED IN COCKPIT ALONG WITH A ODOR OF HOT METAL. APU WAS RUNNING AND APU BLEED VALVE AND ENGINE BLEED VALVES WERE OPEN. REMOVED FAULTY ACM COOLING TURBINE. INSTALLED O/H ACM COOLING TURBINE. OPS CHECK AND LEAK CHECK GOOD. WORK PERFORMED IAW MM 21-51-00.