What is the idling jitter of a4l 1.8t engine after overhaul?

We can only rule out eight common causes of jitter. Of course, Audi is the second item of direct injection turbine, which is not established. It depends on the car.

1, engine jitter caused by spark plugs and cylinder lines

The larger the gap between the anode and cathode of the spark plug, the smaller the surface area of the ignition point, which leads to the decrease of ignition energy required to compress the oil-gas mixture, which leads to the decrease of power, affects power and makes the automobile engine shake. In addition, the aging of the ignition coil may lead to poor flow or leakage of high-voltage electricity, and may also lead to unstable idle speed of the engine and jitter due to power reduction.

2. Engine jitter caused by oil-gas mixture ratio

This phenomenon is very common in old carburetor cars, but if there is something wrong with the computer, it will also happen in EFI cars. The reason is simple and easy to understand. I learned the working principle of internal combustion engine in junior high school, so I don't want to go into details here.

It is worth mentioning that the oxygen sensor is installed near the root of the engine exhaust pipe in the current EFI vehicle, which is an important parameter for the driving computer to control fuel injection. In closed-loop controlled vehicles, the minimum working temperature of the oxygen sensor is 370 degrees Celsius. If the temperature in the exhaust pipe is lower than 370 degrees Celsius just after the vehicle is started, the oxygen sensor will not work, which will cause a temporary judgment error of the driving computer, resulting in an error in the control of oil-gas mixing and ignition time through the actuator.

3, valve, throttle valve and idle valve carbon deposition lead to jitter.

Nowadays, most family cars are equipped with high-speed engines. When this kind of engine needs to shift gears, the engine speed should be 2500 rpm, otherwise it is easy to cause carbon in all areas of the engine. If there is carbon deposit on the valve of the engine and the valve seal is not tight, it will lead to the wrong judgment of the driving computer and affect the oil-gas mixture ratio (air is greater than the normal ratio). Too much carbon deposit can also cause the phenomenon of carbon deposit absorbing gasoline, just like the principle of soil absorbing water is similar, which leads to less gasoline than normal, insufficient power and engine jitter.

4. The difference in the use of each cylinder causes the engine to shake.

As we all know, the common engines are composed of three or more cylinders. After long-term use, the ignition gap and time control of spark plug will be different, but the driving computer can't diagnose such a small deviation and still treat it equally, which leads to errors in practice and theory. Therefore, some cylinders generate less power, resulting in engine jitter. In addition, after the engine is used for a long time, the wear degree of each cylinder liner and piston is also different, which leads to the gap between the cylinder plug ring and the cylinder wall is larger or smaller, especially during cold start, when there is no oil lubrication, the cylinder with large gap will lose part of the high temperature atmosphere, thus reducing the power output and leading to engine jitter.

5, water temperature sensor failure caused by jitter.

The water temperature sensor is also an important basis for the driving computer to judge the running state of the engine at that time. The amount of fuel injected by the fuel injection system is directly controlled by the water temperature inside the vehicle. For example, if the temperature of the engine during cold start is-10 degrees Celsius, but the sensor "tells" the computer that the current temperature is 20 degrees Celsius, then the computer will inject fuel at 20 degrees Celsius, and the fuel injection amount will naturally be less, and the power shortage will naturally appear, so the engine will shake.

6. Other factors leading to jitter

In addition, dirty idle valve body, poor oil products and abnormal operation of idle motor may all cause unstable idle speed of vehicles. This is the previous elimination method.