In reality, there are many reasons for starting difficulty in maintenance. For example, if the injector is defective or the metering unit is faulty, it may cause the vehicle to start difficult or even unable to start, but sometimes the problem may surprise you. Although the case shared by the small rail today is not very complicated, it is very representative, and small problems can also cause the vehicle to fail to start!
Failure case
Basic Information
Vehicle brand: Kamafu shipped
Engine: Yuchai
Computer board: Yuchai Autonomous
Trouble phenomenon: unable to start, abnormal flameout
This car is a van. According to the driver’s feedback, the vehicle suddenly turned off during driving, and then it was difficult to start. The vehicle must be sprayed with starter fluid to start the vehicle, but it will immediately turn off.
Troubleshooting
Step 1: Plug in a diagnostic expert and enter the system to read the fault code. The fault code has only one current fault code P0253. This fault code means that the rail pressure is low, which may be a fault in the metering unit circuit or a fault related to the fuel injector. This situation may result in insufficient engine power, failure to start, or abnormal flameout.
Step 2: The driver gave feedback that the car broke down after a period of time after refueling. It is suspected that there may be a problem with the oil circuit. First, I checked the diesel filter and found that the diesel filter was also a bit dirty. Replace the diesel filter.
Step 3: Check the measurement unit. Remove the metering unit and turn the valve core with the metering unit fork. It is found that the metering unit is not stuck or rusted.
Step 4: Check the oil return of the injector. Remove the fuel return pipe of the fuel injector, start the vehicle, and observe that the fuel return volume of the fuel injector is all too large. Suspected injector failure.
Step 5: Bench test the injector. After removing the fuel injectors, it was found through bench testing that, of the four fuel injectors, three of the fuel injectors had too much oil return, and the other one was directly in a state of loss of pressure and could not maintain pressure.
Step 6: Disassemble the fuel injector that cannot hold pressure for inspection, and it is found that the seal ring of this fuel injector is broken. It seems that the point of failure is the reason. The sealing ring ruptures, which makes it difficult to build pressure, which is the cause of the flame out immediately after a fire.
Step 7: Since there are no accessories, it will take two days for the delivery. The driver said that he couldn’t wait two days for the delivery. So temporarily replace the broken sealing ring with a Bosch sealing ring, and test it again, and found that the oil return is still large. , But it can barely be used.
The eighth step: loading, still difficult to start, but barely able to start, can respond to an emergency.
Step 9: After two days, after the accessories are in place, load the car. Clear fault code, road test, power recovery, troubleshooting!
Summary
The failure of this car is mainly due to the start-up misery caused by the rupture of the injector sealing ring. Of course, the excessive oil return caused by the wear of the injector is also the reason for the start-up difficulty. It can be guessed that the driver’s master may often refuel, and all four injectors have problems at the same time.
Knowledge development
Start-up failure is one of the most common problems we encounter in actual maintenance, but what are the specific reasons for this type of failure? Today, I will mainly summarize the causes of failure to start/difficult to start and some commonly used data streams.
| Failure mode | Point of failure | Specific failure |
| Failure of the metering unit itself | Stuck, rusted, etc. | |
| Oil circuit failure | Low pressure oil circuit failure | Excessive impurities in the fuel tank, filter blockage, pipeline leakage, low pressure oil circuit air intake, overflow valve stuck, etc. |
| High pressure oil circuit leakage | Pressure limiting valve wear and leakage, high pressure plunger wear and leakage, etc. | |
| Injector failure | Excessive oil return from the injector: the needle valve is worn, the sealing ring is damaged, the valve assembly is worn, etc. | |
| Oil pump failure | The fuel pump gear is damaged, stuck, etc. | |
| Air circuit failure | Airway is blocked | Air filter is blocked, exhaust pipe is blocked, etc. |
| EGR valve failure | EGR valve stuck, etc. | |
| Exhaust brake failure | The brake butterfly valve is stuck, the limit gap is too small, etc. | |
| circuit failure | Battery failure | Insufficient power storage, open circuit, short circuit, etc. of power supply wiring harness |
| Starter related faults | Starter relay failure, starter aging, etc. | |
| Metering unit circuit failure | Harness short circuit, open circuit, etc. | |
| Rail pressure sensor failure | Sensor failure, wiring harness short circuit and open circuit, etc. | |
| Injector drive circuit failure | Solenoid valve drive circuit failure | |
| Computer version failure | Problems with the computer version, abnormal power-on, data problems, etc. | |
| Power supply module failure | Shared sensor circuit fault effect with rail pressure sensor | |
| Abnormal start signal | Such as T50 signal, neutral clutch switch failure, etc. | |
| Sync exception | Sync sensor failure | Crankshaft, camshaft itself is damaged or contaminated, etc. |
| Sensor harness failure | Sensor harness open circuit, short circuit, etc. | |
| Sensor installation gap failure | Installation clearance is not in the range of 0.5-1.5MM | |
| Signal board failure | Signal plate is missing teeth, damaged and polluted, etc. | |
| Synchronization timing error | Synchronization timing adjustment error, etc. |
Unable to start, difficult to start Common data stream:
| Reference data stream | Remarks |
| System voltage | Normal system voltage range: small car: 11.6V-14.8V: large car: 23V-25V |
| T15 status | T15 is the ON position of the key switch. This problem may cause the ECU to be unable to power on, or the injector may not be added. |
| T50, start relay control signal | Determine whether the ECU receives a start signal and whether to allow the engine to start. |
| Rail pressure | Rail pressure above 200bar |
| Synchronize | Synchronization or non-synchronization, whether the fuel injector power-on conditions are met, and different system identifications are different. |
| Actual fuel injection | This data stream is used to determine whether the ECU powers up the injector. |
| Neutral, clutch switch state | These switches are abnormal, some of them will cause failure to start, and some will cause delay of starting |
| Assistant start switch, assistant stop switch | Especially if the stop switch under the car is abnormal, it will cause the engine to stop abnormally and even fail to start the car. |
| Water temperature, intake air temperature, oil temperature | Judge whether the temperature is too low to start, or the temperature is too high, and the engine overheating protection is abnormally stalled |
| Warm-up state | Especially when the ambient temperature is low and cold start is difficult, you need to pay attention |
