What was found
JUST PRIOR TO BEING CLEARED FOR TAKEOFF, EXPERIENCED A VISIBLE WHITE SMOKE IN THE COCKPIT. THE ODOR APPEARED TO BE SULFUR TYPE ODOR. AFTER ABOUT 10 SECONDS IT DISSIPATED AND COULD NOT BE ISOLATED AGAIN WITH PAC OR ENGINE BLEED SYSTEMS. VERIFIED ODOR. REMOVED COCKPIT ACM. FOUND HEAVY OIL AND SOOT IN ACM AND DUCTING. CLEANED ALL DUCTING. REPLACED COCKPIT ACM. RE-INSTALLED ALL LINES AND PLUMBING. R & R COCKPIT COALESCER SOCK. ALL SYS OPERATIONAL, LEAK AND SNIFF CHECKED SATISFACTORY. NO ODOR OR SMOKE IN ACFT AFTER 30 MINUTES OF RUNNING SYSTEMS. COMPLETED IAW MM 21-51-00.