The reasons for black smoke emitted by electronic fuel injection diesel engines may involve multiple aspects. The following is a detailed analysis of this phenomenon:

　　1、 Incomplete combustion

　　Fuel supply issue: Uneven or excessive fuel supply to each cylinder, as well as insufficient intake air, are important factors leading to incomplete combustion. Excessive fuel supply can prevent the fuel from fully burning in the combustion chamber, resulting in black smoke.

　　Atomization and injection time: Poor fuel atomization and premature injection time can also affect combustion efficiency, leading to the production of black smoke. Poor atomization means that the fuel has not formed sufficiently fine particles to mix well with the air; If the injection time is too early, it may cause the fuel to stay in the cylinder for too long, increasing the risk of incomplete combustion.

　　2、 Air filter issue

　　If the air filter is severely dirty, it will block the flow of air, resulting in insufficient air entering the cylinder, which in turn affects the combustion effect and produces black smoke. After removing the air filter, observe the exhaust smoke color. If the black smoke situation improves, it can be determined that the air filter is dirty.

　　3、 Fuel injector malfunction

　　The spray quality of fuel injector directly affects the atomization effect of fuel. If the spray quality of a cylinder injector is poor, the combustion efficiency of the cylinder will be reduced, resulting in black smoke. By conducting a cylinder by cylinder fuel cut-off test, it can be determined which cylinder's injector has a problem. When a cylinder loses fuel, if the engine speed decreases and the black smoke significantly decreases, it indicates that there is a malfunction in the fuel injector of that cylinder.

　　4、 Other factors

　　Fuel supply time: Early fuel supply time can also cause fuel to stay in the cylinder for too long, increasing the risk of incomplete combustion. Therefore, it is necessary to regularly check and adjust the fuel supply time.

　　Air intake pipeline issue: If there is a leak or blockage in the air intake pipeline, it can also affect the circulation of air and combustion efficiency. It is necessary to start the engine and check if there are any abnormal sounds or deformations in the intake pipes.

　　In general, the reasons for black smoke emitted by electronic fuel injection diesel engines may include incomplete combustion, air filter problems, injector failures, and other factors. Solving such problems requires careful inspection and maintenance of relevant components to ensure the normal operation of the engine and reduce pollution emissions.