THE BLACK SMOKE IN THE EXHAUST IS MAINLY CARBON PARTICLES FROM INCOMPLETE COMBUSTION OF FUEL. THEREFORE, EXCESSIVE FUEL SUPPLY IN THE FUEL SUPPLY SYSTEM, REDUCED AIR VOLUME IN THE INTAKE SYSTEM, POOR SEALING OF THE COMBUSTION CHAMBER COMPOSED OF THE CYLINDER BLOCK, CYLINDER HEAD, AND PISTON, AND POOR INJECTION QUALITY OF THE FUEL INJECTOR CAN ALL CAUSE INCOMPLETE FUEL COMBUSTION, RESULTING IN BLACK SMOKE EMISSIONS FROM THE EXHAUST. THE MAIN REASONS FOR EMITTING BLACK SMOKE FROM EXHAUST ARE AS FOLLOWS:1. THE HIGH-PRESSURE OIL PUMP SUPPLIES TOO MUCH OIL OR THE OIL SUPPLY OF EACH CYLINDER IS UNEVEN2. POOR VALVE SEALING CAUSES AIR LEAKAGE AND LOW CYLINDER COMPRESSION PRESSURE3. THE AIR FILTER INTAKE DUCT IS BLOCKED AND THE INTAKE RESISTANCE IS HIGH, RESULTING IN INSUFFICIENT INTAKE AIR VOLUME4. SEVERE WEAR OF CYLINDER LINER, PISTON, AND PISTON RING5. POOR OPERATION OF FUEL INJECTOR6. ENGINE OVERLOAD OPERATION7. THE FUEL SUPPLY ADVANCE ANGLE OF THE FUEL INJECTION PUMP IS TOO SMALL, AND IT IS MOVED TO THE EXHAUST PROCESS AFTER THE COMBUSTION PROCESS8. FAILURE OR MALFUNCTION OF GASOLINE ELECTRONIC FUEL INJECTION SYSTEM CONTROL, ETCFOR ENGINES EMITTING BLACK SMOKE, IT CAN BE CHECKED AND ELIMINATED THROUGH HIGH-PRESSURE FUEL PUMP CALIBRATION, INJECTOR INJECTION TEST INSPECTION, CYLINDER COMPRESSION PRESSURE MEASUREMENT, INTAKE DUCT CLEANING, ADJUSTMENT OF FUEL SUPPLY ADVANCE ANGLE, AND DIAGNOSIS OF GASOLINE ELECTRONIC INJECTION SYSTEM FAULTS.