As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING FLT, SMOKE IN CABIN, DURING SLOW CRUISE FLT OVER FIRE TRAFFIC AREA, PERFORMED QRH ITEMS, REMOVED SMOKE FROM CABIN. DEPARTED THE FTA TO KCDC LANDED WITHOUT FURTHER PROBLEMS. MX TROUBLESHOT SMOKE IN CABIN TO BE COMING FROM RT ENG. AFTER EXTENSIVE TROUBLESHOOTING OF R/H ENGINE AND AIR CONDITIONING SYSTEM AND COMPONENTS. FOUND REGULATING VALVE NEXT TO ENVIRONMENTAL CONTROL UNIT (ECU) STUCK IN OPEN POSITION. THIS CONDITION ALLOWED FOR UNRESTRICTED P3 AIR TO OVERHEAT ECU AND BURN OFF OIL CAUSING SMOKE AND HIGH DUCT TEMPS.