Another component that cannot be missing in the high-pressure common rail system of diesel engines is the high-pressure common rail pipe.
The high-pressure pump sends the diesel to the high-pressure common rail pipe, and the oil pressure is measured again.
Ensure that the oil pressure is within a reasonable range before delivering diesel fuel to the injector for injection.
The composition of the common rail pipe is much simpler than other fuel components. One end of the common rail pipe is a pressure relief valve.
When the pressure is too high, return the oil to reduce the pressure, and the common rail pressure sensor measures the pressure value of the high-pressure oil circuit.
The other is the interface connected to each injector.
If the signal error is caused by a sensor failure, it is much easier to repair.
Remove the sensor and use a multimeter to measure the voltage value of the power supply pin and the loop pin. The voltage point is about 5V as normal. If it is below 5V, the sensor is damaged.
Or directly replace it with a normal sensor. If the fault disappears, the sensor is damaged.
1.If there is no problem with the sensor, you need to check the sensor to the ECU wiring harness plug 1.
And measure the continuity between any two points of the rail pressure sensor’s power contact pin, loop contact pin, and signal contact pin.
If there is no problem with the pressure sensor circuit, you need to check whether the fuel metering unit is faulty.
The opening of the metering unit does not meet the fuel supply demand, which will also result in low common rail pressure.
If it is too large, the oil supply is too high and the pressure is high.
Pull out the metering unit plug on the high-pressure oil pump and measure the resistance value of its two contacts.
Its resistance value should be between 2.0-5 ohms.
2.There is air in the oil circuit. The air in the oil circuit will cause part or no diesel in the engine oil circuit.
At the same time, the fault code of the rail pressure closed-loop control mode will be activated, causing the engine to be difficult to start or unable to start.
After draining the air in the oil circuit and checking the inlet point for repair, the fault can be repaired.
Generally, the air inlet points are mostly due to poor sealing at the tubing joints and damage to the gaskets.
The overflow valve is stuck and normally open, the plunger of the high-pressure pump is worn, and the oil capacity of the pump decreases; internal pressure relief, etc.
1.If there is no air in the oil circuit, the engine still cannot be started, and the malfunction of the oil circuit is involved.
At this time, you need to check the actual pressure build-up in the common rail pipe when the engine is started.
If the actual rail pressure value is smaller than the set rail pressure value and the duration is longer, it means that the rail pressure cannot be established.
The ECU cannot command the injector to inject fuel, causing the engine to fail to start.
Check the oil circuit and components in front of the common rail pipe to see if there is any blockage or damage, resulting in poor oil supply.
2.Check whether there is leakage in the oil circuit behind the common rail pipe, which causes the actual pressure of the common rail pipe to fail to reach the set rail pressure.
This situation is generally due to the lack of tight seal between the high-pressure connecting pipe and the injector.
And the fuel inlet of the injector returns directly to the return pipe of the injector without passing through the injector, so that the actual rail pressure cannot reach the set rail. Pressure.