Working principle: The fuel metering valve is a key component with a high failure rate in the Bosch common rail high-pressure oil pump. In most cases, unnecessary replacement of the entire pump can be avoided by accurately locating the fault location and type and individually disassembling, cleaning, or replacing the fuel metering valve.
The fuel metering valve is a proportional solenoid valve, generally installed at the oil inlet position of the high-pressure oil pump, and is controlled by the PWM signal output by the ECU; the ECU controls the opening of the fuel metering valve by changing the duty cycle of the PWM signal to control the inlet plunger. The amount of fuel is used to control the pressure of the common rail pipe.
Different models of Bosch common rail electronically controlled diesel engines have slightly different fuel metering valve structures, characteristics, installation positions, and electrical interface forms depending on the type of high-pressure oil pump used and the specific control strategy. When repairing and replacing Be sure to pay attention to the difference, especially according to the different characteristics of the default state, that is, when the power is off, the fuel metering valve is divided into two types: normally open type and normally closed type. In practical applications, it can be judged based on whether there is a pressure relief valve on the common rail pipe: Generally, commercial vehicle platform engine common rail pipes have pressure relief valves, and their fuel metering valves are normally open; passenger car platform engine common rail pipes have pressure relief valves. There is no pressure relief valve, and its fuel metering valve is normally closed.
For the normally open fuel metering valve, its default working state is normally open, and the flow rate is maximum when it is not energized. The current characteristics of the normally closed type are exactly the opposite.
Common failure modes and failure analysis
- The fuel metering valvecircuit is open or short-circuited (the connection circuit to the ECU is faulty)
a.Turn on the fault light b. Generate corresponding fault codes: P0251 (Fuel metering valvedrive failure - open circuit), P0254 (Fuel metering valvedrive failure - short circuit to power supply), P0253 (Fuel metering valve drive failure - short circuit to ground), P160E (main relay 1 drive circuit failure - short circuit to power supply) or P160F (main relay 1 drive circuit failure - short circuit to ground); c. The controller increases the fuel supply of the high-pressure oil pump; d. The fuel pressure is too high and pressure relief The valve flushes open; e. The diagnostic instrument shows that the rail pressure is 700-760 bar; f. The engine speed is limited, and the throttle still works within the speed limit range.
- The fuel metering valveand its connector are damaged (abnormal internal electrical connection failure)
Improper operations during use, maintenance, disassembly, transportation, and assembly may cause the fuel metering valve and its electrical connector to suffer from bumps, deformation, damage to the internal structure, or even leakage, leading to abnormal electrical connections.
- The connector connection between the fuel metering valveand the ECU wiring harness is abnormal.
The connector pins are bent, broken, aged, worn, rusted, structurally failed, etc., as well as the connector has water ingress, resulting in abnormal connector connections.
- Abnormal driving current and working status offuel metering valve
a.Turn on the fault light b. Generate the corresponding fault code: P025D (Fuel metering valveAD channel signal failure - voltage is extremely high), P025C (Fuel metering valveAD channel signal failure - voltage is extremely low), or P0252 (Fuel metering valve drive failure - over-temperature); c. The controller increases the fuel supply of the high-pressure oil pump; d. The fuel pressure is too high and the pressure relief valve opens; e. The diagnostic instrument shows that the rail pressure is 700-760 bar; f. The engine speed is limited, but the limit throttle still works within the speed range.
- The fuel metering valveis stuck - stuck in the small opening position
a.The rail pressure is lower than the target value and the engine power is insufficient; b. The following fault codes may be generated: P1011 (rail pressure closed-loop control mode fault 0--rail pressure is lower than the target value), P0087 (rail pressure closed-loop control mode fault 3--rail pressure is lower), or P1019 (rail pressure closed-loop control mode fault 12--rail pressure is lower than the target value).
- The fuel metering valveis stuck - stuck in the wide opening position
a.The rail pressure is higher than the target value. When the vehicle accelerates or goes uphill, the pressure relief valve is prone to open; b. The following fault code may be generated: P1013 (rail pressure closed-loop control mode fault 2--the rail pressure is higher than target value), P0088 (rail pressure closed-loop control mode fault 4--rail pressure is too high), P1014 (rail pressure closed-loop control mode fault 7--overrun mode fuel supply is too large) or P1018 (rail pressure closed-loop control mode fault 10 --The fuel supply is too large).
- The fuel metering valvecore is worn and not sealed
When the car is going downhill or pushing backward, the pressure relief valve is prone to open.
Summary: For stuck or damaged fuel metering valves caused by oil quality problems, after repairing or replacing the fuel metering valve, clean and qualified fuel must be replaced at the same time; in addition, for normally closed fuel metering valves, when a line failure occurs, the fuel metering valve is fully closed, and there is no pressure relief valve on the common rail pipe, and the engine will not start.
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