When introducing fault diagnosis to the electronic control system, don't forget to perform basic inspection first. For example, before attempting to diagnose the failure of the fuel injection system controlled by the electronic control unit, make sure that the intake line has no leakage, valve timing, and ignition timing. If these unfavorable phenomena exist, the engine's anti-load alternation ability is poor, and may be extinguished in the case of sudden changes in working conditions, such as accelerated flameout, brake flameout, open air conditioner flameout, and stall stall.
1. Some vehicles have intermittent faults that are difficult to diagnose, except when the car is inspected.
2. When checking for untimed idle speed failure, sometimes it is necessary to change the spark plug.
3. When the air flow meter is suspected to be bad (such as the air flow meter hot line is too dirty; the internal circuit connection solder joints fall off, poor contact, etc.), the oscilloscope can be used to check the air flow signal voltage waveform. Gently tap the air flow meter housing with a screw handle while the engine is running and observe the oscilloscope. If the waveform changes greatly or the engine stalls, replace the air flow meter. Some air flow meters have loose internal connections, which can cause sudden changes in the voltage signal, which can lead to flameout. This test must first determine the contact of the harness connector by vibration.
4. When the intake pressure sensor is suspected to be defective, the sensor vacuum hose should be inspected first to see if it is broken or bent. Is it sometimes leaking or sometimes leaking, so that the intake pressure sensor signal is normal and not normal? The engine is turned off when the accelerator pedal is closed.
5. Also check the sensors that have a large influence on the fuel injection amount, such as the coolant temperature sensor and the oxygen sensor. The coolant temperature sensor not only has an influence on the fuel injection amount, but also one of the signals for correcting the ignition advance angle, so it should also be taken seriously. Sometimes the oxygen sensor signal voltage of some models does not change, which is likely to cause the engine to stall when accelerating.
6. If there is a poor acceleration in the high-speed driving process and then turn off the flame, it is necessary to focus on checking the oil circuit; if it is suddenly turned off during the high-speed driving, it will focus on finding the circuit, and whether the high-pressure spark is too weak is a must-check item. one.
7. Sudden flameout and intermittent flameout should also check the engine speed and crankshaft position sensor of the main sensor that controls ignition.
8. Failure symptom simulation test method. The most difficult situation in troubleshooting is faulty, but there are no obvious signs of failure. In this case, a thorough failure analysis must be performed and then simulate the conditions and circumstances that are the same or similar to those in the event of a user's vehicle failure. No matter how rich the maintenance personnel experience, no matter how skilled his technique is, if he diagnoses the failure symptoms without verification, he will ignore some important things in the maintenance work, which will definitely lead to the malfunction of the vehicle.
In the failure symptom simulation test, the failure symptom must be verified, and the fault location or part must be found. In order to do this, before the pre-connection test and the start of the test, the range of the circuit in which the failure may occur must be reduced, and then the failure symptom simulation test is performed to judge whether the circuit to be tested is normal, and the failure symptom is also verified.
1) Vibration method. When vibration may be the cause of the failure, the vibration method can be used for the test. The basic test methods are mainly:
1 connector. Gently rock the connector vertically and horizontally,
2 wiring. Gently swing the wiring vertically and horizontally. The connector's connector, the vibration bracket, and the connector body that passes through the opening are all parts that should be carefully inspected.
3 parts and sensors. Use your finger to pat the part with the sensor and check for flameout, as shown in Figure 7-1 c. Remember not to force the relay, otherwise the relay may be opened.
2) Heating method. Some faults only occur during hot cars, which may be caused by heat from the parts or sensors involved.
3) Water dripping method. When some faults are generated in a rainy or high-humidity environment, water can be sprayed on the vehicle to check for malfunctions.
4) Fully connected method of electrical appliances. When it is suspected that the fault may be caused by excessive power load, all electrical equipment on the vehicle can be connected to check for malfunction.
Related Industry Knowledge
- Engine technology features
- Engine winter maintenance problem
- How the engine works
- Engine fuel consumption is too large
- Diagnosis and elimination of engine fuel consum...
- Other factors affecting excessive fuel consumpt...
- Engine automatic flameout failure
- The running part of a general vehicle is compos...
- Three typical structural forms of general-purpo...
- Analysis and troubleshooting of the deviation o...
- How to judge steering rack oil leakage
- Check the possible oil leaks of the steering rack
- What is the Reasons of oil leakage from the ste...
- Steering rack oil spill emergency treatment method
- What is the maintenance method of steering rack...
- The danger of steering gear oil leakage
- How to break down steering gear