Why is a large vehicle emitting black smoke?

[LukeLee]

Excessive black smoke from diesel engine exhaust is mostly caused by incomplete combustion due to uneven or excessive fuel supply to each cylinder, insufficient air intake, poor atomization, or premature injection timing. Here are methods to identify the cause of black smoke emission: 1. Observe the exhaust smoke color: Remove the air filter and observe the exhaust smoke color. If the black smoke condition improves, the issue is caused by severe contamination of the air filter. 2. Check the fuel supply timing: Verify if the fuel supply timing is too early. If it is, adjustments should be made. 3. Check cylinder fuel supply: During engine operation, conduct a fuel cut-off test for each cylinder. When a cylinder's fuel supply is cut off, if the engine speed decreases, black smoke significantly reduces, and knocking sounds weaken or disappear, it indicates excessive fuel supply to that cylinder. If the engine speed changes slightly and black smoke disappears, it suggests poor spray quality from that cylinder's injector. After identifying the faulty cylinder, inspect the injector. If necessary, replace it with a new injector for comparison. If the issue disappears with the new injector, it confirms the original injector is faulty.