2016 FORD EXPLORER XLT V6 TI-VCT FLEX FUEL VEHICLE (FFV). EXHAUST ENTERS CABIN DURING ACCELERATION. PUTRID ODOR OF EXHAUST RESEMBLES A FOUL BLEND OF VOMIT, ROTTEN EGGS, BURNT HAIR, BURNT WAX. HEADACHE AND HORRIBLE SMELL LINGERS IN SINUSES CONTINUES TO DAY FOLLOWING EXPOSURE. STENCH IS MUCH WORSE UNDER HEAVY ACCELERATION AND/OR DRIVING UPHILL WITH REAR A/C ON HIGH FAN SPEED. FORD SERVICE ACKNOWLEDGED WIDE-SPREAD PROBLEM PERFORMED TSB 17-0044 SEALING UNDERBODY SEAMS, REPROGRAMING REAR A/C AND REPLACING EXHAUST COMPONENTS. TSB 17-0044 IS INEFFECTIVE AND PROBLEM PERSISTS. 1. FORD HAS NOT ISOLATED SOURCE OF EXCESSIVE CARBON MONOXIDE (CO), HYDROCARBONS (HCS) AND NITROGEN OXIDES (NOX). IS ENGINE DEFLECTION UNDER ACCELERATION IMPACTING EXHAUST MANIFOLDS CAUSING LEAKAGE IN PIPE JOINTS? IS RICH FUEL MIXTURE IN ENGINE WITH UNBURNED FUEL PRODUCING ELEVATED CATALYTIC TEMPERATURES DAMAGING MANIFOLDS OR JOINTS? ARE FFV ENGINES FITTED WITH UNDERSIZED OR FAULTY CATALYTIC CONVERTERS? 2. EXHAUST SYSTEM FAILS TO EXPEL EXHAUST AWAY FROM VEHICLE. FORD ACKNOWLEDGES AS EVIDENCED BY TSB 17-0044 REPLACING MUFFLERS AND EXHAUST TIPS. 3. EXHAUST GASSES POOL IN BUMPER COVER AND NUMEROUS CAVITIES UNDER BODY. 4. AIR CONDITIONING SYSTEM FANS ACTIVELY PULL EXHAUST INTO THE VEHICLE LIKELY THROUGH AIR EXTRACTOR VENTS IN QUARTER PANELS. FORD ACKNOWLEDGES AS EVIDENCED BY TSB 17-0044 REPLACING AIR EXTRACTOR VENTS AND REPROGRAMMING REAR A/C TO SLOW OR HALT FANS UNDER VARIOUS BRAKING SCENARIOS.