Symptom: a BMW 740 sedan, equipped with straight row of strong cylinder engine, but the engine is unstable, rapid acceleration and slow acceleration are not on the oil, and refueling when the fire back, exhaust pipe black smoke, after adjustment, cleaning Nozzle and gasoline filter, the fault remains the same.
    Failure reasons: the engine is unstable, exhaust pipe black smoke, indicating that the mixture in the engine cylinder combustion is not sufficient, this phenomenon is caused by many reasons. When the engine is working properly, the mixture is fully combusted, producing a lot of it
    Heat and promote the piston work, emissions are mainly water and carbon dioxide, so the exhaust is basically colorless and tasteless, the engine is not normal, the exhaust gas contains a lot of carbon monoxide, hydrocarbons and a variety of particles, and black, rapid acceleration When more obvious.
    Troubleshooting and inspection: In the above circumstances, you should first check the spark plugs are excessive carbon deposition, electrode ablation and other anomalies, if not, and then check the cylinder pressure, generally should be greater than 1.2 × 10Pa. If the cylinder pressure is too low, the mixture will not be adequately compressed and can cause poor combustion. At this time should check the cylinder pad, valve, piston ring, analysis to determine the reasons for leakage. If none of the above steps are abnormal, check the engine control system.
    The theoretical value of the air-fuel ratio "A: F" is 14.7: 1, and the air-fuel ratio should be maintained at the theoretical level in other working conditions when the cold start, rapid acceleration or high power output is required. Oxygen sensor by measuring the oxygen content in the tail gas, in a certain range to correct the fuel injection, the formation of closed-loop fuel injection control. (TPS), intake manifold absolute pressure sensor (MAP), air flowmeter (MAF), water temperature sensor (ECT), etc., should be checked for the main components of fuel injection. The rate of change of the TPS signal reflects the acceleration state of the vehicle, which should be mixed to increase the output power while reducing the ignition advance angle to prevent deflagration. It can be seen that the MAP acts as a vacuum advance angle in the carburetor and Power control valve two components of the role of MAP in the case of idle, the output voltage should be between 1V-1.4V, MAP on the fuel injection plays a decisive role, if it is a problem, or in its back-end intake (Such as the intake manifold interface pad damage, etc.), Duff to ECM to provide the wrong signal to make the engine work is not normal, ECF also determines the fuel injection, when the engine operating temperature is low, should increase the fuel injection If the engine temperature is already normal, and the ECT sensor still gives the ECM a low temperature signal, the concentration of the mixture is too high and the engine is not working properly.