Foreword
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The engine is one of the most important parts of a car, and it powers the car's walking. There are many types of automobile engines, and the engine failures of the automobile are also various. If the failure of the automobile engine will affect the driving of the automobile, the serious situation will endanger the safety of the driver. Therefore, it is necessary to understand the diagnosis and elimination methods of automobile engine failures to ensure the safety of driving and prolong the service life of the engine.
First, the diagnosis and analysis of common faults of crank connecting rod
1. Deformation of cylinder block and cylinder head
1.1 Fault phenomenon
1 engine exhausted white smoke. 2 When running at idle speed, open the water tank cover to see bubbles in the water tank. 3 cylinders are depressed.
1.2 Causes of failure
When the cylinder is cast and machined, there is residual stress. Due to insufficient aging treatment of the parts, the internal stress is large, and the internal stress is redistributed at high temperature. 2 The force generated by the reciprocating motion of the crank-link mechanism acts on the cylinder block, causing the cylinder to be pressed, bent and twisted, causing the cylinder block to warp and deform. 3 When tightening the cylinder head bolts, do not tighten in the specified order, the torque is too large or uneven, or remove the cylinder head at high temperature. 4 The engine is operated under high speed and large load conditions for a long time, and the lubrication is insufficient, the shaft is burned, and the shaft is deformed, and the center line of the bearing housing hole is changed.
2. Cracks in the cylinder block and cylinder head
2.1 Fault phenomenon
1 engine exhausted white smoke. 2 When the idling is running, open the water tank cover to see that the water tank is bubbling and the three cylinders are depressed.
2.2 Causes of failure
1 The cylinder block and the cylinder head water jacket have a thin wall thickness. 2 The scale is concentrated too much and the heat is not good. The 3 cylinders are frozen and cracked, the heat and cold are sharply changed, and the collision is vibrated. For example, the exhaust valve seat of the cylinder head belongs to the weak part of stress concentration. The heat insulation of the scale makes the heat dissipation condition further deteriorate, and the thermal stress is too large, and cracks are easily generated under the action of stress concentration.
4 Residual stress effects during casting. 5 The inertia of the engine during high-speed operation, thermal stress, and the interaction of the cylinder block with alternating stress cause cracks in the water jacket wall. 6 valve seat cylinder liner setting times too many, improper press-fit process or excessive interference
2.3 Troubleshooting check
Testing cylinder block and cylinder head
3, cylinder head ablation
3.1 Fault phenomenon
1 The engine of the car (the working principle of the car engine) is not running smoothly, and the exhaust pipe has a "sudden and sudden" sound. 2 The engine performance deteriorates, the power is reduced, and the speed cannot be increased. 3 adjacent two cylinders of helium, the cylinder pressure is low, sometimes the intake pipe is tempered, and the exhaust pipe is fired. 4 cylinder gasket water channel at the helium, resulting in air bubbles in the engine radiator. 5 The coolant leaks into the cylinder, discharging white smoke, and the engine is difficult to start. 6 The coolant leaks into the crankcase, which raises the oil level and deteriorates. 7 The engine temperature is high, sometimes there is a leak at the edge of the cylinder head outside the engine.
3.2 Causes of failure
1 The cylinder head bolt tightening force is not uniform, or the tightening force is not enough. 2 The cylinder block and the cylinder head joint surface are deformed. 3 Engines often operate under heavy loads, premature ignition, engine overheating, knocking, etc. 4 cylinder gasket itself quality problems.
3.3 Troubleshooting
Replace the cylinder head gasket in time and grind the cylinder head plane if necessary.
Second, the analysis and elimination of common faults in winter
There are three common faults in the cold state of winter: cold car is not easy to start, cold engine engine idling and cold car acceleration are poor. Many maintenance personnel do not know how to start when they encounter these faults. Below we have three kinds of "cold cars". The fault is analyzed and solved.
1.1 Fault phenomenon and analysis
(1) Cold car is not easy to start
If the engine has a fault that is difficult to start, the cause of the fault generally includes: 1 starting system failure, such as insufficient battery power, damage to the starter, or failure of the starter circuit. 2 engine mechanical failure, such as air intake pipe leakage, poor sealing between the piston and the cylinder, and the valve closing is not strict, resulting in low cylinder pressure. 3 Excessive carbon deposits in the back of the intake valve and in the intake pipe cause the injected gasoline to be adsorbed by the coke and cannot enter the combustion chamber. 4 engine management system failure, such as weak speed sensor signal, incorrect water temperature signal, and poor line contact. 5 There is a fault in the ignition system, such as too much carbon deposit in the spark plug or incorrect gap, leakage of the high voltage line, and damage to the ignition coil. 6 The oil supply system is faulty, such as the fuel system is kept under pressure, the injector is leaking or blocked.
(2) Cold car engine idling jitter
When the engine is cold-started, if there is no cold-speed idling or unstable speed failure, the faults generally include: 1 engine mechanical failure, such as low cylinder pressure. 2 Intake system failure, such as air intake pipe leakage. 3 Excessive carbon deposits on the back of the intake valve and in the intake pipe. 4 engine management system failure, such as water temperature, intake air temperature signal is incorrect, the line is faulty. 5 There is a fault in the ignition system, such as too much carbon deposit in the spark plug or incorrect gap, high voltage line, leakage of the distributor cover, and damage to the ignition coil. 6 The oil supply system is faulty. For example, if there is too much carbon deposit inside the injector, the injector is not tightly closed or blocked. (3) Cold car accelerates "carriage"
Although many auto manufacturers' instructions indicate that the cold start can be started without warming up after starting, I believe that if the engine can be slightly warmed up for 3 to 5 minutes after starting, it will be of great benefit to the engine. Because this can reduce the mechanical wear of the engine, the small displacement engine can make the starting power sufficient. If there is a sudden acceleration after a cold start, there will be a phenomenon of “carriageâ€. If the phenomenon of “carriage†is serious, the cause of the failure is generally: 1 engine mechanical system failure, such as low cylinder pressure, resulting in a decrease in engine power, which is more prominent in the cold state. . 2 Excessive carbon deposits in the back of the intake valve and in the intake pipe cause the injected gasoline to be adsorbed by the coke and cannot enter the combustion chamber. 3 engine management system failures, such as water temperature, intake air temperature signal is incorrect, line faults, etc. 4 There is a fault in the ignition system, such as too much carbon deposit in the spark plug or incorrect gap, high voltage line, leakage of the distributor cover, damage to the ignition coil, etc. 5 The oil supply system is faulty. For example, if there is too much carbon deposit inside the injector, the injector is not tightly closed or blocked.
1.2 failure measures
The diagnosis of the above three faults should be carried out according to the principle of first electric power, first simple and then complicated. If the engine has the "three heat faults" that the hot car is not easy to start, the hot car idling and the hot car accelerates poorly, it should be excluded first. . The diagnosis steps are as follows: 1 Check the appearance of the engine, check whether the vacuum tube and harness connector are disconnected, and whether there is air leakage, leakage, oil leakage and water leakage. 2 Use the troubleshooter to query the fault code and data flow. 3Measure with a multimeter, oscilloscope, etc. 4 Determine the cause and component of the fault according to the above inspection, and repair or replace the accessory. 5 After the fault is removed, use the above equipment to test again. 6 Reproduce the fault occurrence conditions for testing or road test.
Third, diesel engine fault diagnosis and troubleshooting
Diesel exhaust smoke
Observing the exhaust color of the diesel engine and judging whether the operation of the diesel engine is faulty is a simple and effective method.
When the engine is at normal working temperature, its exhaust smoke color should be colorless or light gray. The so-called colorless is not completely colorless. It can't be colorless like a gasoline engine, but it is accompanied by a light gray in the colorless. This is normal. Exhaust smoke color; exhaust smoke may be heavier when the engine is idling, and may be heavier at high speed and high load. Pay attention to the normal exhaust smoke color to have a clear understanding of abnormal exhaust smoke.
(1) Exhaust smokes black smoke. Black smoke from diesel engine exhaust is mainly caused by excessive fuel, poor formation of combustible mixture or imperfect combustion.
(2) Blue smoke. Exhaust blue smoke, generally caused by the engine used for a long time, slowly began to burn the oil, as the blue smoke is aggravated, burning more and more oil, you should consider repairing the diesel engine. Sometimes the fuel is mixed with moisture, or there is water leaking into the combustion chamber, causing a change in combustion, and the diesel engine will light blue smoke.
(3) White smoke. White smoke means that the exhaust smoke is white, unlike colorless, white is white of water vapor. White indicates that the smoke contains moisture or contains unburned fuel components. When the diesel engine is running in cold weather, the engine temperature is low, the exhaust pipe temperature is also low, and it is normal for the steam exhaust gas to condense into water vapor to form white exhaust smoke. When the engine temperature is normal and the exhaust pipe temperature is normal, the white smoke is still discharged, indicating that the engine is not working properly. The cause of the failure may be: the fuel contains too much water; the fuel injection pump pressure is too low; the injector failure causes the fuel Caused by poor atomization in the combustion chamber, poor formation of combustible mixture, and the like.
(4) Gray smoke. Light gray smoke, diesel engine work is still normal, but the color of the smoke is gray or close to black is not normal, in addition to the above reasons for black smoke, there may be reasons for poor air intake, that is, the air supply is not good. When the intake air filter is removed, the exhaust smoke changes from deep to light or even to no color, that is, the air filter is clogged, and the cause of poor air intake should be checked.
Conclusion
Along with the development of science and technology, more and more electronic devices are on the car, and various sensors have appeared one after another. It is impossible to completely solve all car engine failures by experience alone. It is necessary to detect the vehicle by using the detecting instrument, so that the vehicle fault can be easily and quickly found, and blind disassembly and assembly can be avoided, and the structure of the vehicle (automobile engine maintenance) must be known during the inspection.
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