Diagnosis Of Truck Parts

After the truck was repaired, the fault recurred, which is a problem we often encounter in maintenance; in dealing with such problems, we should jump out of the failure phenomenon and analyze the root cause of the failure.

Engine Diagnosis

Fuel injector failure, such as too small fuel injection at idle point;
L sensor problems, such as signal drift of water temperature sensor and intake air temperature sensor, resulting in low idle fuel injection;
Intake and exhaust pipelines, such as blocked intake and exhaust, resulting in the poor intake of the engine;

Tightness of the cylinder, such as loose sealing of diagnosis inlet and exhaust valves, failure of exhaust braking in the cylinder, failure of piston ring, etc;
Fuel pipeline problems, such as air leakage in fuel pipeline, resulting in air entry in the high-pressure pipeline, etc;

Synchronization timing problems, such as single speed sensor starting, abnormal synchronization signal, etc;
Computer board ECU problems, such as abnormal data and ECU electrical aging.

Read the fault code with a diagnostic expert diagnosis
The display system is normal, which proves that it is not the cause of the fault code and the engine cannot be started.
Use a diagnostic expert to read the data stream, which is the data stream when starting the engine. From the data stream, it can be preliminarily determined that the synchronization and rail pressure are normal

Unplug the water temperature sensor
Unplug the water temperature sensor and increase the fuel injection quantity during starting; Start the engine again and the engine will not stop.

Tips of diagnosis:

For a normal system, the conditions for fuel injector power are: synchronous speed and rail pressure above 200bar
Replace ECU
After replacing the ECU, the engine can start normally and the fault is solved.
Fault postscript:
After a month, the truck failed to start again. After troubleshooting, it was found that the fault point the truck was that the fuel injector could not be powered on. Replace a new ECU and solve the problem. Another month later, ECU failure occurred again.
In just two months, burning three computer versions will certainly not be a problem with the quality of the computer version. It can be preliminarily determined as the problem of the whole vehicle line. Use the oscilloscope to collect the voltage of the power supply (K01 / k03 / K05), T15, and T50.

When collecting T15 harness with oscilloscope, it is found that the harness voltage fluctuation here is abnormal.
The highest peak voltage collected is 64V, which is more than twice the normal voltage value (normally not more than 32V), indicating that there must be a problem with the harness here.
The line change of this vehicle is serious, and the problem can not be solved after flying the line again. Therefore, it is recommended that the driver replace the engine and chassis harness.
After replacing the harness, the fault is solved.

case analysis of diagnosis

After the fault case is finished, I believe there is no problem for you to check whether the fuel injector is powered on. However, for the following problems, I also wants to analyze them with you.
Case analysis
After the fault case is finished, I believe there is no problem for you to check whether the fuel injector is powered on. However, for the following problems, xiaorail also wants to analyze them with you.

How is the voltage fluctuation of T15 harness generated?

According to the requirements of the Bosch harness, the power supply of ECU is directly from the battery and cannot be connected with other loads, especially high-power loads such as generators and starters. When a high-power load shares the power line with ECU, it may lead to violent voltage fluctuation, which is caused by electrical components such as capacitance and inductance in electrical equipment.
Therefore, the fault is because the load of the whole vehicle is connected to the ECU power supply, resulting in the internal burning of the ECU.
For this fault, why is there no flying wire, but the method of directly replacing the harness of the whole vehicle?
After the harness of the whole vehicle is disordered, it is difficult to restore it. If it is not restored well, it will bring other problems, and the computer version may be burned again. Therefore, in case of such problems, it is recommended to replace the harness of the whole vehicle directly.

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