There is carbon deposit in the exhaust pipe. What happened?

Generally speaking, incomplete combustion will lead to carbon deposition. Check whether there is a fault code first, and there will usually be a diagnosis result. If there is no testing equipment, generally, first check whether the throttle has carbon deposit cleaning, and then check the spark plug to make sure there is no problem. Then check the circuit oxygen sensor, and then check the three-way catalyst of the exhaust pipe.

If there is no problem, check whether the valve leaks, whether the cylinder pressure reaches the standard, and whether the piston ring and cylinder liner are greatly worn. After removing the mechanical problems, the problems are whether the fuel injection quantity of the oil circuit is too large, whether the air flow sensor is faulty, and then whether there is a problem with the gasoline.