Author:Site Editor Publish Time: 2020-09-10 Origin:Site
Once the electronically controlled engine fails, the fuel injector and fuel metering unit will be replaced frequently. Among them, the suction control valve is often due to the valve body being worn and stuck, which often leads to failures such as difficulty in establishing rail pressure, difficulty in starting, intermittent flameout, and speed limit at 1500 rpm.
Failure strategy of suction control valve
When the suction control valve is damaged, the engine control computer is equipped with a self-protection program. The engine control computer has been detecting the working conditions of the fuel metering unit) to limit the speed and torque output. Regarding the damage of the fuel metering unit and whether the engine can be started, this mainly depends on the control strategy of the model and system:
The fuel Inlet metering valve fails and the engine cannot be started
When the fuel metering proportional solenoid valve fails such as stuck and cannot be opened, the high-pressure fuel cannot enter the fuel rail. This type of failure is mostly caused by impurities in the fuel. The fuel metering proportional valve can be cleaned; fuel metering ratio The connection line between the solenoid valve and the ECU is disconnected, causing the ECU to fail to control the fuel metering proportional solenoid valve, so the engine stalls or fails to start. Note: The fuel metering solenoid valve used in this car is normally closed
Simple failure case analysis
For example, during the downhill deceleration process of an electronically controlled common rail engine, the engine will enter the deceleration cut-off mode, that is, it will cut off the fuel injection of the injector. At this time, the fuel metering solenoid valve should be completely closed to prevent the fuel rail pressure from continuing. Elevated. However, if the metering unit is stuck and cannot be completely closed, the rail pressure will continue to rise, causing the common rail excessively high drain valve (pressure limiting valve) to be forcibly opened. At this time, touch the return line temperature by hand Obviously high, the engine will enter the fail-safe state and the engine power speed will be limited.
Oil metering unit inspection
1. In view of the domestic fuel quality problems, most of the failures related to the damage of the fuel metering unit are due to card issuance; in addition, there are also some problems that appear on the circuit, such as short circuit and open circuit.
2. Detecting fuel metering unit requires professional tools. For example, fuel metering unit adjusting device can adjust the driving current of driving metering unit, but some people can use simple methods to detect the quality of fuel metering unit.
3. The direct method is to use the data flow item of the diagnostic instrument to view the relationship between the drive change of the fuel metering unit and the rail pressure. With the increase of throttle opening, the follow-up situation of rail pressure changes.
4. Use a fuel metering unit with a DC stabilized power supply with the same driving voltage to detect the quality of the fuel metering unit. Generally, the working current of the dosing unit is below 2000Ma. Gradually adjust from 0 mA to increase the driving current while blowing the metering unit with the mouth. Valve hole, to see whether the ventilation volume increases with the increase of current. Of course, this can only roughly judge the working condition of the measuring unit.
5. Listen to the sound to judge,
6. Resistance measurement, Bosch's resistance value is generally 2.3-3.1 ohms, and the maximum current is 1.8A.
Matters needing attention
1. The fuel metering unit must be kept clean after disassembly, and there must be no dust and foreign matter pollution
2. The fuel metering unit cannot be disassembled casually.