When an automobile engine is not working properly but self-diagnosis system does not display a fault code, it is especially necessary to rely on operator's inspection and judgment to determine nature of fault and location of fault. guilt. The author now summarizes common automotive engine failures as follows:
1.1 Engine won't start
(1) Malfunction: turn on ignition, turn ignition key to start position, engine does not start.
(2) Possible causes of failure:
A. Starting system failure causes engine to not rotate or rotates too slowly: ① Insufficient battery charge, loose electrode rod clamp, or severe electrode rod oxidation, ② Main circuit fuse blown, ③ Ignition switch failure. ④ Starter failure ⑤ Start circuit is disconnected or poor contact in circuit connector.
B. Ignition system malfunction: ①Ignition coil not working properly resulting in weak or no high voltage spark ②Igniter malfunction ③Incorrect ignition timing.
C. Fuel injection system malfunction: ①No fuel in fuel tank; ② The fuel pump does not work or oil pressure in pump is too low; fuel pressure regulator not working properly; filter is dirty.
D. Air intake system malfunction: ① Faulty idle control valve or its control circuit ② Damaged air tube of idle control valve or leaking connection ③ Faulty air mass meter.
E. ECU malfunction.
(3) Methods and stages of diagnosis and exclusion.
①When starting gear is engaged, neither starter nor engine can rotate, and this should be checked depending on malfunction of starting system. First of all, check storage condition of battery, as well as connection and contact of poles; if battery is OK, check starting circuit, fuse and ignition switch; ② Press accelerator pedal to middle open position, and then turn on starter. If engine can start at this time, this means that problem is with idle control valve and its circuit malfunction or a leak in air intake pipe. next step is to be tested; ③ Perform a visual inspection. Check if there is air leakage in inlet pipe; check if hoses and their connections are intact; check for air leaks or rupture of hose of crankcase ventilation device; ④ Check for high voltage sparks. If high voltage spark is abnormal, check high voltage line, ignition coil, distributor and electronic igniter; ⑤ check ignition sequence is correct; ⑥ Check oil supply to oil supply system. In case of confirmed presence of breakthroughs in fuel tank, check fuel supply pressure to fuel line; ⑦ checkthose ignition timing and ignition sequence of each cylinder; ⑧Check working condition of fuel pump switch installed on airflow. meter; ⑨ check each cylinder spark plug working condition; ⑩ Check ignition timing. If ignition timing is not correct, further check ignition timing control system;?B11?Check ECU power and operating conditions to determine if it is an ECU malfunction
1.2 Engine stop error
(1) Malfunction phenomenon: When engine is running, speed fluctuates from high to low. This phenomenon is an engine stop phenomenon, and its malfunction is called engine stop error.
(2) Causes of failure: Causes of high and low engine speeds include fuel injection system failure, ignition control system failure, and intake system failure. The most common causes of failures are:
① There is an air leak in intake system. For example, air leakage from various hoses and connections, PVC valve, exhaust gas recirculation system, oil dipstick socket, oil filter cap, etc.; ② The air filter element is too dirty; ③ Air mass meter is abnormal; ④ The oil supply pressure of fuel injection system is unstable. For example, fuel line is deformed, system line connection is poor, fuel pump pressure is insufficient, fuel pressure regulator is unstable, fuel filter is too dirty, circuit breaker contact is shaking, etc.; incorrect ignition timing; oil tank and temperature timer do not work well; ⑦ ECU malfunction.
(3) Diagnosis and elimination methods and steps: ①Check whether there is air leakage in intake pipe. Check hoses and connections, PVC valve tube, EGR system, oil dipstick socket, oil filter cover; ② Check oil supply pressure. Check if there is too little fuel in fuel tank, and check if pressure in fuel line is unstable. The specific method is same as when engine cannot be started; ③ check if air filter element is too dirty; ④ check ignition timing; ⑤ check spark plugs of each cylinder; ⑦ check airflow output voltage. counter and its connection with change in operating state of engine; ⑧ Check condition of fuel injection injector; ⑨ Check working condition of ECU.
1.3 Engine idle error
(1) Malfunction: The engine runs normally when engine is running at medium speed or higher. When idle speed is or close to idle, idle speed is unstable or even stalls, which is poor idle speed. guilt.
(2) Cause of failure: low idle speed is usually caused by air intake system and fuel injection control system, and sometimes badi idle speed can also be caused by a mechanical engine failure. Common causes of low idle are: ① air leak in intake system; ② cold start fuel injector and temperature control switch not working properly; ③ abnormal oil supply pressure to fuel injection system; ④ Injector failure causes injection Poor atomization quality ⑤ ECU failure.
(3) Diagnosis and troubleshooting methods and steps: ① Check for air leakage in intake pipe, PVC valve hose and oil dipstick; ② Check if air filter element is too dirty; Check if time control switch works. fine; ④ Check if pressure in fuel system is too low; ⑤ Check injection nozzle; ⑥ Check cylinder pressure and valve clearance if necessary; ⑦ Check ECU.
1.4 Lean Blend
(1) Signs of failure: engine speed is unstable, power is obviously insufficient, and there are back flashes, then it can be considered that engine has a failure due to too lean mixture.
(2) Malfunction causes: ① Air leakage in intake system; ② Faulty cold start injector and temperature time switch; ③ Too low fuel pressure in system; ④ The fuel injector is defective. stuck or blocked; ⑤ Malfunction of air mass meter; ⑥ Faulty water temperature sensor; ⑦ Throttle position sensor failure; ⑧ ECU malfunction.
(3) Diagnosis and troubleshooting methods and steps: ① Check air intake system for air leaks; ② Check cold start fuel injector timing switch; ③ Check fuel injector for blockage and card failure; ④ Check air. flow ⑤ check water temperature sensor, ⑥ check operation of throttle position sensor, ⑦ check input and output signals of each ECU terminal.
1.5 Acceleration error
(1) Failure Symptoms: When engine accelerates slowly from low speed to high speed, engine runs perfectly fine, but when accelerating quickly, engine speed changes slowly, sometimes choking or stalling.
(2) Reasons for failure: ①Intake system air leakage problem; ②The system oil supply pressure is too low; ③The ignition voltage is too low; ④Ignition time too late; ⑤Cylinder pressure is too low. too low or valve clearance too small; ⑥ Throttle position sensor does not work properly; ⑦ ECU malfunction.
(3) Methods and steps for diagnosis and exclusion: ① Check intake system for air leakage ② Check high-voltage spark ③ Check ignition timing is normal ④ Check system oil supply pressure ⑤ Check operation of throttle sensor, whether it is normal; ⑥ Check if signals of each ECU terminal are normal; ⑦ Check valve clearance andworking pressure in cylinder, if necessary.
2 Engine Diagnosis and Troubleshooting Diagram
2.1 Flowchart for diagnosing and troubleshooting when engine cannot be started
Electronic motor cannot rotate or rotates very slowly. The main reason is that battery or starting system is defective. To eliminate it, you can check battery and starting system: If crankshaft rotates normally and engine cannot start, main reason is fuel injection system is faulty, sensors, actuators, electronic control units and their circuits are faulty, and they can be eliminated using method presented in Figure 1:
2.2 Diagnosis and Troubleshooting Flowchart for Poor Acceleration or Flameout
2.3 Low idle or burnout
The main cause of low idle or flame failure is a failure of idle control system, which can be corrected according to procedure shown in Figure 3:
3 Inspection and Maintenance Precautions
3.1 Motor service points
(1) The gasoline variable injection system places high demands on purity of gasoline, and deleaded gasoline should be used, brand and quality of which fully comply with requirements. The fuel filter must be replaced regularly to keep foreign particles in fuel from clogging fuel injector.
(2) Use power supply strictly as required. When installing battery, polarity must be observed, otherwise electronic components will burn out.
(3) Try to avoid strong vibration of computer, and do not allow water to enter parts (components) of electronic control system.
(4) If battery does not start normally due to loss of battery power, battery should be charged in time or replaced with a new battery, and try not to use jump circuit method to start engine.
(5) Do not wash microcomputer control box and other electronic devices with water. The humidity of room where engine is stored should not be too high, and try not to wash floor with water in summer.
(6) Protect microcomputer system from strong mechanical shock and vibration.
(7) The motor should be kept away from electrical equipment that may emit electromagnetic fields to avoid strong electromagnetic fields in space affecting microcomputer system.
3.2 Electronic Fuel System Checkpoints
(1) When ignition key is turned on and engine is not running, warning light should come on. After starting engine normally, warning lamp should go out, if it does not go out, this means that computer's self-diagnosis system has detected a malfunction or an abnormal phenomenon. During this time, battery must not be disconnected from circuit to prevent loss of fault codes and related information stored in microcomputer. The failure of electronic petrol injection system should be judged by number of flashes of warning lamp or output fault code, and fault code should be read using special equipment.
(2) Before checking and repairing oil supply system, first remove battery ground wire.
(3) The electric fuel pump is controlled not only by ignition switch, but also by a switch inside air mass meter. After ignition is turned on, fuel pump will run continuously only when engine is in normal running or starting status and air mass meter detects air flow signal or microcomputer determines ignition speed and signals. Its output oil pressure is higher than that of general oil supply system. After damage, it can only be replaced with an original model electric fuel pump.
(4) During maintenance, regardless of whether engine is runningor not, with ignition on, never turn off any running electrical devices. Since these devices often have a certain amount of inductance, if their operating current is suddenly cut off, a high instantaneous voltage will be generated in circuit, which will cause serious damage to electronic devices.
(5) If arc welding is required, power line of electronic control unit must be disconnected.
(6) When overhauling microcomputer and sensors and actuators connected to it, operator must remove static electricity from body in advance, and must also wear an iron metal strap, wrap one end around wrist, and attach other end to body so that avoid damage to microcomputer system caused by static electricity.