Why does the LeFeng engine fault light come on?
Common car engine faults and troubleshooting methods
When the car engine is not working properly and the self-diagnosis system does not output a fault code, it is especially necessary to rely on the operator's inspection and judgment to Determine the nature of the fault and its location. The author now summarizes the common faults of automobile engines as follows:
1.1 The engine cannot start
(1) Fault phenomenon: Turn on the ignition switch and move the ignition switch to the start position, but the engine cannot start. .
(2) Possible reasons for the failure:
A. Starting system failure prevents the engine from turning or turning too slowly: ① Insufficient battery storage, loose electrode post clamp or electrode The piles are severely oxidized; ② the circuit main fuse is broken; ③ the ignition switch is faulty; ④ the starter is faulty; ⑤ the starting line is open or the line connector has poor contact.
B. Ignition system failure: ① The ignition coil is not working properly, resulting in weak or no high-voltage spark; ② Ignition failure; ③ Incorrect ignition time.
C. Fuel injection system failure: ① There is no fuel in the fuel tank; ② The fuel pump does not work or the pump oil pressure is too low; ③ The fuel pipe leaks and deforms; ④ The circuit breaker relay is disconnected; ⑤ The fuel pressure regulator works Defective; ⑥The fuel filter is too dirty.
D. Intake system failure: ① Idle speed control valve or its control circuit failure; ② Idle speed control valve air pipe rupture or joint leakage; ③ Air flow meter failure.
E.ECU failure.
(3) Diagnosis and elimination methods and steps.
① When the starter gear is turned on, neither the starter nor the engine can rotate. Check the starter system for faults. First, check the battery storage condition and pole connection and contact condition; if the battery is normal, check the starting circuit, fuse and ignition switch; ② Depress the accelerator to a medium opening position, and then turn on the starter. If the engine can start at this time, it means that the fault is a fault in the idle speed control valve and its circuit or a leak in the intake pipe. If it still cannot start when the accelerator is depressed to a medium opening position, the next step of inspection should be carried out; ③ Perform a visual inspection. Check whether there is air leakage in the intake pipeline; check whether each hose and its connection is intact; check whether there is air leakage or rupture in the crankcase ventilation device hose; ④ Check for high-pressure sparks. If the high-voltage spark is abnormal, check the high-voltage wire, ignition coil, distributor and electronic ignition; ⑤ Check whether the ignition sequence is correct; ⑥ Check the oil supply of the oil supply system. After confirming that there is leakage in the fuel tank, check the fuel supply pressure in the fuel pipe; ⑦ Check the ignition timing and the ignition sequence of each cylinder; ⑧ Check the working condition of the fuel pump switch installed on the air flow meter; ⑨ Check each cylinder The working condition of the spark plug; ⑩ Check the ignition timing. If the ignition timing is incorrect, the ignition timing control system should be further checked; B11 Check the power supply and working conditions of the ECU to determine whether it is a fault of the ECU.
1.2 Engine Stall Fault
(1) Fault Phenomenon: When the engine is working, the speed rises and falls suddenly. This phenomenon is the engine stall phenomenon, and the fault is called engine stall. Fault.
(2) Reasons for the failure: The reasons for the sudden high and low of the engine speed include the failure of the fuel injection disk system, the failure of the ignition control system, and the failure of the air intake system. Common causes of failures include the following:
① There is an air leak in the air intake system. Such as air leakage in various hoses and connections, air leakage in PVC valves, air leakage in the EGR system, air leakage at the oil dipstick socket, air leakage in the oil filter cover, etc.; ② The air filter element is too dirty; ③ The air flow meter is working Abnormal; ④The fuel supply pressure of the fuel injection system is unstable. For example, the oil pipe is deformed, the system circuit connection is poor, the fuel pump oil pressure is insufficient, the fuel pressure regulator is unstable, the fuel filter is too dirty, the circuit breaker relay contacts are shaking, etc.; ⑤ The ignition timing is incorrect; ⑥ Cold start injection The oil heater and temperature timing switch are not working properly; ⑦ECU failure.
(3) Diagnosis and troubleshooting methods and steps: ① Check whether there is air leakage in the air intake pipeline.
Check each hose and connecting joint, PVC valve pipe, EGR system, oil dipstick socket, and oil filter cover; ② Check the oil supply pressure. Check whether there is too little fuel in the fuel tank and whether the pressure in the fuel pipe is unstable. The specific method is the same as when checking that the engine cannot start; ③ Check whether the air filter element is too dirty; ④ Check the ignition advance angle; ⑤ Check the working condition of the spark plug of each cylinder; ⑥ Check the working of the cold start injector and temperature time control switch ⑦ Check the output voltage of the air flow meter and its relationship with the changes in engine operating conditions; ⑧ Check the fuel injection condition of the injector; ⑨ Check the working condition of the ECU.
1.3 Poor engine idle speed fault
(1) Fault phenomenon: The engine works normally when running at a medium speed or above. When the speed is at idle speed or close to idle speed, the idle speed will be unstable or even stall. phenomenon, that is, poor idle speed.
(2) Cause of failure: Poor idle speed is usually caused by the air intake system and fuel injection control system. In some cases, poor idle speed can also be caused by engine mechanical failure. Common causes of poor idle speed include: ① There is an air leak in the air intake system; ② The cold start injector and temperature control switch are not working properly; ③ The fuel supply pressure of the fuel injection system is abnormal; ④ Injector failure causes injection Poor atomization quality; ⑤ECU failure.
(3) Diagnosis and troubleshooting methods and steps: ① Check whether there is air leakage at the intake pipe, PVC valve hose, and oil dipstick; ② Check whether the air filter element is too dirty; ③ Check cold start fuel injection Check whether the injector and temperature control switch are normal; ④ Check whether the fuel system pressure is too low; ⑤ Check the injection condition of the injector; ⑥ Check the cylinder pressure and valve clearance if necessary; ⑦ Check the ECU.
1.4 Lean mixture fault
(1) Fault phenomenon: The engine speed is unstable, the power is obviously insufficient, and there is backfire, it can be considered that the engine mixture is too thin. Fault.
(2) Reasons for the failure: ① There is air leakage in the intake system; ② The cold start injector and temperature timing switch are faulty; ③ The system fuel pressure is too low; ④ The injector is stuck or blocked; ⑤Air flow meter failure; ⑥Water temperature sensor failure; ⑦Throttle position sensor failure; ⑧ECU failure.
(3) Diagnosis and troubleshooting methods and steps: ① Check whether there is air leakage in the air intake system; ② Check the timing switch of the cold start injector; ③ Check whether the injector is clogged or stuck; ④ Check the working condition of the air flow meter; ⑤ Check the water temperature sensor; ⑥ Check the working condition of the throttle position sensor; ⑦ Check the input and output signals of each terminal of the ECU.
1.5 Poor acceleration fault
(1) Fault phenomenon: When the engine accelerates slowly from low speed to high speed, the engine works completely normally, but during rapid acceleration, the engine speed changes slowly. Sometimes there is wheezing or tempering.
(2) Reasons for the failure: ① There is an air leakage fault in the intake system; ② The system oil supply pressure is too low; ③ The ignition voltage is too low; ④ The ignition time is too late; ⑤ The cylinder pressure is too low or the valve clearance Too small; ⑥ The throttle position sensor is not working properly; ⑦ ECU failure.
(3) Diagnosis and troubleshooting methods and steps: ① Check whether there is air leakage in the air intake system; ② Check the high-pressure spark situation; ③ Check whether the ignition advance angle is normal; ④ Check the system oil supply pressure; ⑤ Check Whether the throttle sensor is working normally; ⑥ Check whether the signals from each ECU terminal are normal; ⑦ Check the valve clearance and cylinder working pressure if necessary.
2 Engine fault diagnosis and troubleshooting flow chart
2.1 Engine cannot start fault diagnosis and troubleshooting flow chart
The electronically controlled engine cannot If the crankshaft rotates normally but the engine cannot start, the main reason is that the battery or starting system is faulty. You can check the battery and starting system for troubleshooting: If the crankshaft rotates normally but the engine cannot start, the main reason is that the sensors, actuators, and electronic controls of the fuel injection system are faulty. If there is a fault in the unit and its circuit, it can be eliminated according to the procedure shown in Figure 1:
2.2 Diagnosis and troubleshooting flow chart of poor acceleration or flameout
2.3 The engine has poor idling speed or stalls
The main reason for poor idling speed or stalling is the failure of the idle speed control system, which can be eliminated according to the procedure shown in Figure 3:
3 Attentions during inspection and maintenance Matters
3.1 Main points of electronically controlled engine maintenance
(1) The controlled gasoline injection system has high requirements on the cleanliness of gasoline, and the brand and quality should be completely Deleaded gasoline that meets the requirements. The fuel filter should be replaced regularly to prevent foreign matter in the fuel from clogging the injectors.
(2) Use the power supply strictly in accordance with the requirements. The polarity must be correct when installing the battery, otherwise the electronic components will burn out.
(3) Try to prevent the computer from being subject to severe vibration, and prevent moisture from infiltrating into the components of the electronic control system.
(4) When the battery is depleted and the engine cannot start normally, the battery should be charged or replaced with a new one in time, and try not to use a jumper circuit to start the engine.
(5) Do not flush the microcomputer control unit and other electronic devices with water. The humidity of the environment where the engine is stored should not be too high, and try not to wash the floor with water in summer.
(6) Prevent the microcomputer system from severe mechanical shock and vibration.
(7) The engine should be kept away from electrical equipment that can emit electromagnetic fields to avoid interference from strong electromagnetic fields in space to the microcomputer system.
3.2 Electronically controlled fuel system inspection points
(1) When the ignition switch is turned on but the engine does not start, the warning light should be on. After the engine starts normally, the warning light should go out. If it does not go out, it means that the computer self-diagnostic system has detected a fault or abnormal phenomenon. At this time, the battery cannot be disconnected from the circuit to prevent the fault code and related information stored in the microcomputer from being lost. The fault of the electronic gasoline injection system should be judged based on the number of flashes of the warning light or the output fault code, and special equipment should be used to read the fault code.
(2) Before performing maintenance operations on the oil supply system, the ground wire of the battery should be removed first.
(3) In addition to being controlled by the ignition switch, the electric gasoline pump is also controlled by the switch in the air flow meter. After the ignition switch is turned on, the gasoline pump will only work continuously when the engine is in normal operation or starting state and the air flow meter detects the air flow signal or the microcomputer detects the rotation speed and ignition signal. Its oil outlet pressure is higher than that of the general oil supply system. After it is damaged, it can only be replaced with the original model of electric gasoline pump.
(4) During maintenance, no matter whether the engine is running or not, as long as the ignition switch is turned on, never disconnect any working electrical device. Because these devices often have a certain inductance, when their working current is suddenly cut off, a high instantaneous voltage will be generated in the circuit, which will cause serious damage to electronic devices.
(5) If arc welding is required, the power supply cord of the electronic control unit should be disconnected.
(6) When overhauling the microcomputer and the sensors and actuators connected to it, the operator must eliminate static electricity on his body in advance. He must wear a metal strap with an iron connection and wrap one end of it around his wrist. , the other end is clamped to the car body to avoid damage to the microcomputer system caused by static electricity.