Possible causes of the opening failure of the pressure limiting valve:
1. Poor oil return;
2. Damage to the rail pressure sensor or its circuit;
3. The fuel metering valve is damaged;
4. Clogged fuel injectors;
5. Pressure relief valve failure;
6. During the operation of the engine, the ignition signal is occasionally lost.
7. The wiring harnesses of the crankshaft and camshaft sensors are inserted in reverse.
8. Crankshaft sensor malfunctions;
9. The two wires of the crankshaft sensor are in reverse position (4G / 4E).
10. Excessive resistance in the low-pressure oil circuit;
11. ECU failure;
12. Throttle circuit (arranged in descending order of fault probability)
Personal suggested inspection steps (arranged according to the probability of the cause of the fault):
1.First of all, we need to determine whether the pressure limiting valve opening fault of the faulty vehicle is occasional or persistent. If it is occasional, it is best to collect the data at the time of the fault by following the vehicle. When collecting data, pay special attention to the changes in actual rail pressure and theoretical rail pressure. If the actual rail pressure of the vehicle is much greater than the theoretical rail pressure at the moment when it is under heavy load, the most likely cause of this fault is poor oil return. If the cause is poor oil return, this fault usually occurs when the engine is under heavy load (full load and uphill).
2. The second way to determine whether the rail pressure sensor is functioning properly can be verified through the following steps: The rail pressure sensor has three wires, namely the ground wire, the rail pressure signal wire (the middle one), and the 5-volt reference voltage wire. Under the condition that the ECU is powered on but the engine does not start and the rail pressure sensor connector is not unplugged, measure whether the voltage of the rail pressure sensor signal wire is within 0.5-0.55V (normal range). If the ECU is powered on but the engine does not start, unplug the contact piece of the rail pressure sensor for measurement. The three normal wires of the rail pressure sensor should be as follows: 5 volts for the rail pressure reference voltage, 5 volts for the rail pressure signal wire, and one ground wire.
In addition to measuring the voltage value of the rail pressure signal line with a multimeter, it can also be obtained through the actual rail pressure voltage value on the diagnostic instrument. According to the above standards, if any abnormalities are found during the inspection, please check the relevant circuit conditions.
3. Thirdly, check whether the fuel metering valve is normal and whether the resistance value of the fuel metering valve is within the normal range of 2.6 to 3.15Ω. If it is within this range, please check whether the driving voltage of the fuel metering valve is 24 volts.
In addition, clues can also be detected from the fuel quantity metering valve set current value on the diagnostic instrument. When the engine is powered on but not started, or when the metering valve is faulty or the circuit is open, the set current value of the fuel quantity metering valve is: 400mA. After startup, its normal current range is approximately 700 to 1500mA.
4. If the ignition signal line of the engine is powered off during operation, the fuel injector will stop injecting due to the power failure. At this time, the engine will rotate due to inertia, driving the fuel pump to increase the fuel that has passed the metering valve and deliver it to the common rail pipe, causing the rail pressure to rise instantaneously and resulting in the pressure relief valve opening. To address this issue, one can determine whether there is a power outage by monitoring the changes in the engine status values while following the vehicle (if the engine status value reaches 48 during engine operation, it indicates a loss of the ignition signal).
5. Additionally, monitor the engine operation parameters and determine whether the fuel injectors are working properly; The parameter of the rail pressure product component can be referred to: the normal range of the rail pressure control product component is -2000 to +2000mm/s. If the rail pressure product component significantly exceeds this range and is accompanied by the appearance of the fault code Rail Pressure Control Mode Fault 7, 10. Then the possibility of the fuel injector getting clogged is relatively high. This situation can also cause the rail pressure relief valve to open when the engine is under heavy load.
6. The above situations are the common causes of pressure limiting valve opening fault. If the problem still cannot be solved after checking all the above five steps, you can continue to check one by one according to the 11 possible causes summarized above.