What are the reasons for black smoke coming from a car?
2 Answers
Black smoke coming from a car can be caused by: 1. Clogged air filter; 2. Excessive fuel system pressure; 3. Air leakage; 4. Reduced vacuum; 5. Insufficient ignition system energy; 6. Poor valve sealing, internal leakage; 7. Excessive clearance between cylinder liner and piston; 8. Incorrect ignition timing, some engine cylinders not working; 9. Faulty oxygen sensor, air flow meter, fuel pressure regulator, intake pressure sensor, or coolant temperature sensor; 10. Damaged cold start injector or ECU computer program; 11. Damaged throttle position sensor or its circuit.
Last time I helped Old Zhang fix his old Passat that was emitting black smoke, the most common issue was a clogged intake. If the air filter hasn't been changed for six months and gets as dirty as a wall, the engine can't breathe properly and will emit black smoke. I've also encountered leaking fuel injectors, where the black smoke pours out like burning firewood. Diesel vehicles need extra attention to insufficient high-pressure fuel pump pressure; improper fuel-air mixture will cause black smoke. By the way, older turbocharged cars should have their EGR valve checked—if it's stuck and exhaust flow is restricted, it's prone to smoking. If you smell a pungent odor, there's an 80% chance the catalytic converter is faulty. This part is expensive but shouldn't be skipped.
