Diesel engine often has mechanical dry friction when it works normally, so in order to ensure the normal operation of the engine, it is necessary to do cold start when the car shake is a common problem of gasoline vehicles. The most fundamental reason for the jitter of cold start or idle waiting is that the combustion in cylinder is not good. If the car does not burn well, it will not provide enough power, and the car will shake. For example, imagine that a foal can pull a car with a force of 100 points, but if it only exerts a force of 60 points, of course, it will not move and shake.
Low ignition energy is the first problem when a car starts cold. The temperature in the engine is not enough, and the temperature of fuel and lubricant is not enough. Therefore, more fuel should be injected to meet the requirements of power when starting cold. The larger the gap between spark plugs, the smaller the ignition energy. At low temperature, the fuel atomization is not good, the fuel needs higher ignition energy. When the car is used for a long time, the spark plug ignition clearance is easy to increase, which leads to the decrease of ignition energy, thus affecting the power performance and making the car jitter.
In addition, aging of ignition coil, aging of high voltage wire of spark plug or leakage of electricity can also lead to the reduction of ignition energy.
1. Inappropriate mixing ratio
The mismatching of oil-gas mixing ratio exists in both open-loop and closed-loop control. In a closed-loop controlled car, the lowest operating temperature of the oxygen sensor is 370 degrees Celsius. If the car is just started, the oxygen sensor will not work because the temperature in the exhaust pipe is less than 370 degrees Celsius. At this time, ECU misjudges, and its control of oil-gas mixing and ignition time by the actuator has errors, which reduces the power output of the car and causes dithering phenomenon.
2. Carbon deposition in valve and inlet
If carbon deposits occur in the valve and intake ports of the engine, the ECU misjudges because the carbon deposits can absorb the appropriate amount of fuel.
The computer actually controls the injection of assumed 100 portions of oil, but only 90 portions actually go into the cylinder, so even if the remaining 90 portions of mixed oil and gas are fully burned, they can not achieve the required dynamic performance, and the jitter phenomenon is unavoidable.
3. Different Cylinder Working Conditions
Similarly, the spark plug of multi-cylinder engine will have the above problems. After long-term use, spark plug ignition clearance and time control will be different, but ECU can not diagnose this deviation, still treat them equally, which results in actual and theoretical errors, and some cylinders produce less power, resulting in jitter.
After long-term use of the engine, the clearance between each cylinder liner and piston will be different in size or in size, that is, some of the clearance is large, and some of the clearance is small. In cold start, there is no good oil lubrication, and the cylinder with large clearance can easily leak high temperature gas from the clearance, thus reducing the power output.