When we encounter abnormal engine jitter, in addition to the air system failure mentioned in the previous article, abnormal rail pressure is also one of the main culprits for engine jitter.

For the investigation of abnormal rail pressure, I believe that all the masters who have seen the oil circuit series courses must be very familiar with it. The main reasons for rail pressure failure are as follows: fuel filter clogging, fuel pump oil pressure insufficient, metering unit stuck, pressure relief valve leaking, and so on.

Abnormal fuel supply pressure will result in excessive or insufficient diesel injection, reduced engine power performance, and engine jitter. When encountering abnormal rail pressure, you can refer to the tenth chapter of “Xiaobai Electric Control Oil Circuit Secrets”, and use the method of fuel pressure detection and low pressure direct connection to quickly locate the fault point. Not much to say, hurry up to practice in a malfunctioning car:

Basic Information

Vehicle brand: Lonking

Engine: Weichai Deutz

ECU: Weichai Autonomous WISE15

Trouble phenomenon: idle speed traveling car

Troubleshooting

Step 1: Use diagnostic equipment to detect that the system is normal and there is no fault code.

Step 2: Check the data stream and find that the engine speed is beating back and forth between 650 r/min and 850 r/min when the engine is idling, the rail pressure changes between 300 Bar and 500 Bar, and the trigger current changes between more than 1100 and more than 1500. The duty cycle is also constantly changing from 12% to 19%.

Step 3: Check the low pressure oil circuit, replace the diesel filter element and the failure remains. Try to replace the crankshaft sensor. The fault persists, and the accelerator pedal signal is also normal.

Step 4: So far, it is suspected that the problem is the oil circuit. There is a normal car of the same model nearby. I decided to replace the overflow valve and try it. At the same time, the metering unit of the problem car was also removed, and I decided to install it on a normal car and try it. First, change the overflow valve and drive the car to a normal speed. Then, after the metering unit is replaced, the normal car also starts to idle and jitter. Therefore, it is judged that it is a metering unit problem. Replacement parts will cause the fault to be resolved.

Fault summary

In this case, the metering unit is stuck. When the metering unit is in a position with a small opening, the trigger current and rail pressure fluctuations of the metering unit are also large. The ECU can hardly control the rail pressure, which causes the rail pressure to be high and low. Touring car.