What knowledge does a car mechanic have?

If you want to be an auto mechanic after graduation, you should master the necessary auto repair knowledge. What are the basic knowledge? The following is the knowledge I have compiled for you as a car mechanic, hoping to help you.

Knowledge possessed by auto mechanics

1. Check the ignition timing (check the initial ignition advance angle)

Inspection method:

1. For the electronically controlled engine, first give the computer a signal to check the ignition advance angle, such as: Toyota short-circuited E1 and TE1 in the engine detection and diagnosis seat; Mitsubishi 4G64 engine should be short-circuited with the brown circular short-circuit connector next to the engine; To make the computer know that the initial ignition advance should be checked. For the 491 series electronically controlled engine, the ignition advance angle that performs the original detection function can be set to a fixed value. The purpose of this is to make the computer remove the timely adjustment of the ignition advance angle and make it fixed at the initial (fixed) position.

2. Use the timing gun to determine whether the ignition advance angle is in the specified position (the computer display value should be consistent with the advance angle of the timing mark at the engine pulley seen by the timing gun;

3. The test results are consistent and normal; Inconsistency indicates improper basic adjustment or mechanical damage (such as 491? The rolling key of crankshaft pulley of ME series models can be detected by this method), and the mismatched parts are installed (crankshaft pulley is installed incorrectly).

2. Check the idle speed (the normal operation of an engine is inseparable from a stable and standard idle speed). Idle speed reflects many problems of the engine;

inspection method:

1. adjustable (7? 5 rpm) is mainly adjusted by screws, and it needs to be based on the original maintenance manual; For example, 2RZ-E engine,

2, non-adjustable (7? 5 rpm) for the computer program settings, there is no artificial adjustable.

3. In case of unstable idle speed and traveling, it is necessary to check that the ignition timing reference position must be correct.

4. Idle speed reaction ①. Whether the oil pressure is normal;

②. Whether the fuel injection is normal;

③ Early or late ignition timing

③ Detection of vacuum degree (vacuum degree is one of the most direct, effective and reliable data reflecting the working quality of an engine);

inspection method: use a vacuum gauge to detect the vacuum degree of the engine intake manifold

1. Connect the vacuum gauge behind the throttle to make the engine run in a normal state and read the vacuum degree.

2. Check the change of vacuum degree by changing the throttle opening at will,

3. Application point of vacuum meter;

①. It can accurately judge whether the valve is not closed properly due to valve damage, (poor valve seal, stuck rocker shaft,)

②. It can accurately judge whether the ignition is early or late;

③ We can see the gas distribution phase in the morning and evening. (For 4G22/2) series, we can check the gas distribution phase (normal is 21 inches of mercury; 17? 19 o'clock means there is a problem? The sprocket and shaft assembly of the intake and exhaust camshafts are not up to standard, and there is a relative displacement phenomenon.)

IV. Check the resistance of spark plugs, high-voltage lines, ignition heads and high-voltage lines of distributors

Inspection methods:

1. Spark plugs suitable for this model should be selected for each model. Cold spark plugs are suitable for engines with high power and high compression ratio; (Jinbei can't use multipole spark plugs, installing wrong spark plugs in Jinbei at a single point will cause computer damage, and Mitsubishi 4G64\63 engine can't use BOSH spark plugs), otherwise it will lead to unexpected failures such as high-speed flameout, closing the throttle and stopping the car. That is, spark plugs should not be mixed, otherwise it will damage the computer and ignition module.

2. Check the spark plug gap (1.2mm for electronic ignition), the combustion color, pay attention to the selection of cold and hot spark plugs, and measure the resistance of the cylinder line (experience: the cylinder line resistance of Jinbei single-point EFI can be used continuously if it is less than 8 thousand ohms);

3. Check the distributor head and distributor cover for serious ablation or leakage; Whether there is water, dirt, improper sensor clearance, loose distributor shaft wear, leading to jitter and poor acceleration, the method mainly depends on observation; Irregular flameout caused by poor sensor signal coil can be detected by tapping the distributor body gently with a tool when the engine is idling to make it vibrate and observe the situation before and after comparison.

V. Analysis of ignition waveform (using special tool ignition oscilloscope)

Inspection method:

1. Use oscilloscope to inspect the ignition system of the engine, the purpose of which is to observe the combustion situation in the engine cylinder and find and analyze problems;

2. The primary, secondary and ignition waveforms can be tested, and the ignition waveforms can be juxtaposed (two cylinders are analyzed and compared) and displayed (four cylinders are compared) to check the combustion work

3. The ignition waveform can check the ignition coil, high voltage line, spark plug, cylinder pressure, rich and lean mixture and low high voltage leakage waveform;

The above inspection is more accurate and faster without disassembling parts; But it requires a higher level of inspection and maintenance personnel.

6. Cylinder pressure, whether the cylinder pressure is normal or not is the primary condition for an engine to work normally;

Inspection method:

1. Check with the cylinder pressure gauge, and the cylinder pressure of the EFI vehicle is generally above 1; 491 is generally 11? 12kg

2. In order to distinguish the fault point when the cylinder pressure is insufficient, a little engine oil can be injected into the piston cylinder barrel to verify whether the difference is the valve or the piston ring.

VII. Detection of valve timing: (The crank angle is used to indicate the opening, closing and duration of the near and exhaust valves, which is called valve timing. ) It represents the mutual positional relationship between the intake valve, exhaust valve and crankshaft.)

Influencing factors:

1. Manufacturing deviation of valve train parts; Or the grinding precision is not enough;

2. Wear or deformation during use,

3. Improper assembly and adjustment

4. Crankshaft timing gear and camshaft timing gear (two camshaft positions of the dual camshaft vehicle itself) do not meet the requirements due to inadequate assembly and maintenance. For example, the timing assembly requirements of 4G22/2 series engines are extremely strict

VIII. Air leakage rate of cylinders (which can explain the problem more accurately than cylinder pressure inspection)

Inspection method:

Hang the hand brake of the forward gear, inject compressed air through the spark plug hole, listen to the exhaust pipe and oil sump for air leakage, and connect the pressure gauge to check the air leakage.

this method is rarely used only when verifying that the valve is not closed properly in a certain cylinder of the engine. The measured cylinder must have the valve fully closed and the piston is at the top dead center. Maintenance knowledge that car mechanics should know

1. Inspection of belt

When starting the engine or driving the vehicle at ordinary times, the belt sounds. One case is that the belt has not been inspected and adjusted for a long time, so it can be adjusted according to normal standards. Another case is that the belt is aging and needs to be replaced.

2. Inspection of air filter

Dirty air filter will cause poor engine operation, excessive oil consumption and damage to the engine, etc. When inspecting the air filter, if less dust is found and the blockage is light, you can use high-pressure air to blow it clean from the inside out and continue to use it. Dirty air filters should be replaced in time.

3. Inspection of spark plugs

Normal insulating ceramics of spark plugs are in good condition. There is no leakage phenomenon. When the spark plug gap is .8+-.mm, the spark is blue and strong. If any abnormality is found, it is necessary to adjust the gap or replace the spark plug.

4. Check the gasoline filter

If the oil supply is not smooth, check whether the gasoline filter is blocked, and replace it in time if it is blocked by foreign objects.

5. Check the engine oil quantity

Park the vehicle on a level road. Pull out the vernier to check the oil quantity. If the oil brightness is within the two markings (f) and (l), it belongs to the normal range; if it is lower than (l). Then the specified engine oil should be added, and the liquid level after refueling should not be higher than (F).

6. Check the coolant level of the engine

Never open the radiator cover when the engine is in a warm-up state, otherwise it may be scalded by spilled coolant or high-temperature steam. After the engine cools down, check that the liquid level of coolant should be between full level and low level, otherwise distilled water or pure water (mineral water is not allowed) or frozen liquid should be added, and the liquid level after adding water should not exceed full level. If it is found that the cooling liquid decreases rapidly in a short time, check whether there is any leakage in the cooling system or go to the maintenance station for inspection.

7. Inspection of brake fluid level

If the brake is between high and low, it means normal. If the brake fluid is close to or below the lower limit, it means that there may be leakage in the system or the brake shoes are worn too much, so you should go to the maintenance station for maintenance in time.

when adding brake fluid, pay attention to adding the same type of brake fluid to prevent damage to the leather cup, and pay attention to protecting the paint to prevent corrosion of the paint surface.

8. Check the liquid level of the clutch master cylinder

The clutch liquid level between the high and low liquid levels indicates that it is normal. If it is lower than the standard line, it may be that the master cylinder or the slave cylinder cup is damaged. When the engine is running, it will be difficult or impossible to shift gears. Please go to the nearest maintenance station for maintenance immediately.

9. Maintenance inspection of the battery

Check whether the battery is firmly fixed. The electrolyte should be between the upper limit and the lower limit. When it is close to the off-line, it should be supplemented with electrolyte or distilled water to the high line in time. Keep the positive and negative cables of the battery in good contact and keep the battery clean and dry. Vehicles that have been placed for a long time should remove the positive and negative cables of the battery. After about half a month's interval, they should be reconnected to start the engine for about 2 minutes. If the power is obviously insufficient, they should be charged in time.

1, tire inspection