Gasoline EFI engine electronic control system fault inspection method Chengdu Panfeng Technology

Fault inspection methods for the electronic control system of gasoline EFI engines Chengdu Panfeng Technology Modern engine technology is becoming more and more mature. With the continuous optimization and advancement of production processes and materials, there are fewer and fewer mechanical failures in the actual use of automobile engine systems. However, there are more failures related to the electronic control system than the mechanical part. The manifestations of faults are almost always mechanical, but in fact they are not necessarily mechanical problems. It can even be said that most of them are not mechanical problems. Using traditional engine fault repair methods to repair engines equipped with advanced electronic control systems cannot eliminate faults. How to identify the essence of a fault from the fault phenomenon is a basic skill that those of us in the automobile industry must master. This article outlines some fault detection methods for the electronic control system of gasoline EFI engines. We will also launch articles on engine troubleshooting methods in the future, so that practitioners can think about problems from more principles and draw inferences about engine fault diagnosis and repair using similar technologies.
.Main faults and causes of the electronic control unit
Defaults in the engine electronic control unit itself and the wiring will cause difficulty in starting the engine or failure to start, unstable idling or even flameout, poor acceleration, black smoke from the exhaust pipe, etc. Fault. The main reason is that the circuit of the electronic control unit is in poor contact, the connectors are oxidized or detached, and foreign moisture enters the electronic control unit, causing damage to the electronic control unit and improper operation during repairs, which burns out the electronic control unit.
.Inspection of the electronic control system
Inspection of the electronic control unit
If the electronic control unit and its control circuit are faulty, you can use the electronic control unit detector of the model or the car electronic control device that is common to each model. unit decoder to check. If these instruments are not available, you can also use a multimeter to measure the voltage or resistance of each terminal on the socket on one side of the electronic control unit to determine whether the electronic control unit and its control circuit are faulty. Using this method to detect faults in the electronic control unit and control circuits must be based on the detailed maintenance technical data of the vehicle being tested. This information includes the standard voltage values of each terminal in the wiring harness plug of the model's electronic control unit and which sensors and actuators in the control system are connected to each terminal under different operating conditions of the engine. If an abnormality is found during the test, it indicates that there is a fault and the connection part of the actuator is abnormal, it indicates that the electronic control unit is faulty and the connection part of the sensor is abnormal, it may be that the sensor circuit is faulty.
The common methods of inspection are as follows.
) Voltage measurement method. According to the connector diagram and the normal voltage data and measurement conditions of each wiring point, use a multimeter with high input impedance to check.
①The battery voltage should be above.
② Remove the wiring harness connector, but keep the connector connected for voltage check.
③ Keep the ignition switch in position.
④ A multimeter should be inserted from the side of the wiring harness connector, or a pin should be inserted to measure the voltage between each terminal and the ground.
⑤The measurement results should be compared with the standard value. If there is a big difference from the standard value, it means there is a fault in the control wiring harness.
)Resistance measurement method
① Unplug the wire plug and measure the normal resistance value according to the connector diagram and each wiring point.
② Use a high-impedance digital multimeter and try to use a high-ohm block for measurement to prevent the measurement current from damaging the internal components and causing the fault to expand.
③The connector diagrams of various car models are different, but the symbols used represent the voltage and resistance values of each contact in the same car series, and can only be used as a reference for other car models.
Inspection of the sensor
) Coolant temperature sensor
When the coolant temperature sensor itself or the circuit is not working properly, the following malfunctions may occur: ① Difficulty starting the engine ② Unstable idling ③ Easy to stall.
The main causes of coolant temperature sensor failure are as follows.
①Scale and oil scale are the main causes of misalignment of the coolant temperature sensor. Inaccuracy of the coolant temperature sensor will cause the air-fuel ratio to be inaccurate, which will cause difficulty in cold starting, unstable idling, poor acceleration, or black smoke from the exhaust pipe (fuel consumption).
② Failure refers to open circuit or continuity. When the circuit is open, its resistance is infinite, resulting in an increase in the amount of fuel injection. When the idle speed is too high, when it is turned on, the resistance is zero, causing the mixture to no longer be enriched, making it difficult to start a cold start, and there is no fast idle speed during a hot start. For this reason, some have a cut-off function. Once this function fails, it is corrected to the normal water temperature, causing the injector to inject fuel at the normal water temperature.
The precision of the coolant temperature sensor has a great impact on the amount of fuel injection. When the mixture is too rich or too lean, the coolant temperature sensor should be disassembled and inspected. The detection method is as follows.
①Measure the resistance between the coolant temperature sensor wiring. When the coolant temperature is ⒛℃, its resistance value should be ~℃, and it should be...~. If the measurement results do not meet the specified requirements, the coolant temperature sensor should be replaced.
②Ignition switch. When the coolant temperature is ℃, measure the voltage between the ignition switch and the ignition switch. It should be .~. If it does not match, further inspection should be carried out.
) Intake air temperature sensor
When the intake air temperature sensor itself or the wiring is not working properly, the following malfunctions may occur: ① poor engine performance ② unstable idle speed ③ easy stalling ④ increased fuel consumption or rich fuel.
The main reasons for the failure of the intake air temperature sensor are as follows.
① Use a bad air filter.
② Improper operation by electrical maintenance personnel (use the scratch test method to find faults).
When checking the intake air temperature sensor whose structure is similar to the coolant temperature sensor, the method of checking the coolant temperature sensor can be used. Under normal circumstances, when the temperature is ℃, the resistance value of the resistor is about ~ ℃. When the temperature is ℃, the resistance value is about .~. If the measurement results do not meet specifications, the sensor should be replaced. When the blast air temperature sensor installed in the air flow meter is damaged, the air flow meter should be replaced.
)Oxygen sensor
Abnormal oxygen sensor signal will cause increased engine fuel consumption. The oxygen sensor signal line must be in good contact and well insulated, because its output power supply is weak and has very little energy.
There are two types of oxygen sensors: heated (three-wire type) and non-heated (single-wire type). For heating type, the heater resistance should be checked. The oxygen sensor inspection method is as follows.
①Voltage inspection method. Use a digital multimeter with high input impedance to measure the oxygen sensor voltage.
Start the engine and measure the voltage at the terminals on or off the diagnostic box. It is normal.
Remove the gasoline pressure regulator hose from the intake manifold and vent the upper part of the pressure regulator to the atmosphere. Start the engine after blocking the manifold joint, and measure the voltage at the terminals at normal idle speed. The voltage at the terminals should be above.
②The resistance value of the cold resistance of the oxygen sensor heating wire is about ~. If it does not meet the requirements, the oxygen sensor should be replaced.
Other sensors include throttle position sensor, crankshaft position sensor, camshaft position sensor, knock sensor, vehicle speed sensor, Hall synchronization signal sensor, etc.