As the weather gets colder, many vehicles experience difficulties in cold starting, idling vibration after cold starting, poor acceleration after cold starting, and other malfunctions. Until the water temperature of the vehicle rises, all of the above malfunctions disappear. What is the reason for this? The answer is that there is too much carbon buildup inside the engine. Uneven fuel quality and congested urban road conditions are both causes of carbon buildup.
The causes of a cold start of the car are as follows
Low temperature of engine
The temperature inside the engine is not enough, and the temperatures of both the fuel and lubricating oil are not sufficient. Therefore, more fuel should be injected during cold starts to meet the power requirements. At low temperatures, the fuel atomization is poor, leading to a decrease in ignition energy and thereby affecting the power, causing the car to shake. The aging of the ignition coil, the aging or leakage of the high-voltage wire of the spark plug, can also lead to a decrease in ignition energy.
Excessive carbon deposits in the valve and intake port cause difficulty starting the vehicle when it is cold
Due to the fact that carbon deposits can absorb a certain amount of fuel, the ECU may make incorrect judgments. The computer actually controls the injection of 100 parts of oil and gas, but only 90 parts (10 parts are absorbed by carbon deposits) actually enter the cylinder. Even if the remaining 90 parts of mixed oil and gas are fully burned, it still cannot achieve the required power, and the shaking phenomenon is inevitable.
When there is too much carbon deposit inside the engine, the gasoline injected by the cold start injector will be absorbed by the carbon deposit in large quantities, resulting in a too-thin mixture of cold start, making it difficult to start the engine. It is not until the gasoline absorbed by the carbon deposit reaches saturation that it is easy to start the engine. After starting the engine, the gasoline adsorbed on the carbon deposit will be sucked into the cylinder by the vacuum suction of the engine for combustion, which makes the mixture thicker. The mixture of the engine is sometimes thin and sometimes thick, causing the idling to shake after cold start.
The lower the temperature, the greater the amount of oil needed for cold start, and the more the existence of carbon deposits will affect whether the cold start is successful or not. Carbon deposits can have adverse effects on the normal operation of the engine in every part. For example, when there is too much carbon deposit in the combustion chamber, it will increase the compression ratio of the engine, forming many hot spots, which may cause premature ignition and deflagration, shortening the service life of the engine; When there is carbon deposit on the working surface of the valve and its seat, it may cause valve closure failure and leak gas, resulting in difficult engine start, reduced power output, and easy erosion of the valve.
The carbon deposits on the guide and stem of the valve will accelerate wear on the guide and stem, and may even cause the stem to become sticky and stuck within the guide, leading to valve stick faults. Carbon deposits in the groove of the piston ring will reduce the clearance between the piston ring and cylinder wall, possibly leading to failure of the piston ring and cylinder wall to maintain compression, resulting in engine damage. Carbon deposits on the injector may cause different injection amounts for each cylinder, leading to engine vibrations. Excessive carbon deposits on the spark plug may cause it to fail due to electrical leakage, leading to engine vibrations. Excessive carbon deposits on the throttle plate can also cause starting difficulties and idling vibrations.
In order to make the engine work better, we should pay more attention to maintaining the vehicle and regularly cleaning the carbon deposits in various places. Only in this way can the vehicle start smoothly when the weather gets cold, eliminating the troubles of the owner’s friends.
The working conditions of each cylinder are different
After long-term use, the spark plug’s ignition gap and time control may vary, leading to errors between actual and theoretical values. As a result, some cylinders produce less power, which can cause shake.
Water temperature sensor failure
If the engine is cold-started at -10 degrees Celsius, but the sensor “tells” the computer “the current temperature is 20 degrees Celsius,” then the computer will inject fuel according to the conditions at 20 degrees Celsius, which will naturally result in less fuel and cause shake.
Improper mixing ratio
In closed-loop controlled vehicles, the minimum operating temperature of the oxygen sensor is 370 degrees Celsius. If the vehicle is just started and the temperature in the exhaust pipe cannot reach 370 degrees Celsius, the oxygen sensor will not work. At this time, the ECU makes a mistake, and its control of the fuel-air mixture and ignition time through the actuating mechanism leads to errors, which reduces the power output of the vehicle and causes shake.
Other reasons of difficulty starting a cold car:
1.The air flow meter is dirty, resulting in a decrease in intake air;
2.The EGR (Exhaust Gas Recirculation) valve is not working properly, introducing exhaust gas at idle speed. The idle motor controls the bypass intake port to regulate the amount of air intake. If the voltage is low, the operation may not be fully functional.
3.The oil quality is too poor to achieve the corresponding calorific value, resulting in a smaller power output of combustion. All the four factors can lead to poor combustion in one cylinder during cold start or idling, thus causing engine shake.
4. In winter or cold weather, high viscosity oil (10W or 5W suitable for winter) is used.
5. Excessive carbon deposits in the intake system and at the root of the intake valve cause the concentration of the mixture to be too dilute during cold starting;
6. The throttle is severely dirty and the intake air volume is insufficient;
7.The starter’s rotational speed does not meet the requirements;
8.The contact resistance of the battery’s connection wires is too large;
9. The battery’s power is insufficient;
10. The viscosity of the transmission’s lubricating oil is too high, causing excessive engine operation resistance;
11.The engine’s cylinder compression pressure is insufficient; c
12.The high-voltage ignition system – the spark plug’s performance is poor, unable to generate an ideal electrical spark to ignite the mixture;
13.The spark plugs are not reasonably installed;
14.The engine coolant temperature sensor malfunctions.
Solution to the difficulty of cold starting a car
To solve the problem of cold start difficulties, we need to first check whether there is excessive carbon deposition on the throttle and idle speed valve. Excessive carbon deposition can easily block the idle air passage and cause intake airflow obstruction. Therefore, if there is excessive carbon deposition, we need to clean it. Additionally, we need to check whether the engine control system’s water temperature sensor is working normally. Both of these problems can lead to the occurrence of cold start difficulties.
The reasons for the deterioration of starting conditions at low temperatures are as follows: the viscosity of the oil increases, reducing starting speed; the low temperature causes a decrease in the ion concentration of the battery, reducing speed and reducing ignition energy; and the low temperature leads to a decrease in molecular activity, making it difficult to form a flammable mixture. Therefore, cold start difficulties occur. It is recommended to step on the clutch before ignition.
Troubleshooting method for difficult start-up of engine when it is cold and normal start-up after warm-up
When the engine is cold, it is difficult to start and requires multiple starts before it can operate. After warming up, it starts normally. A common cause is insufficient air charging coefficient and the engine has too low idle speed during cold start and warm-up (high idle speed is required during cold start and warm-up to ensure smooth operation). It is important to check whether the coolant temperature sensor has failed and whether the idle stepping motor has seized.
(1) Check the engine speed indicator after starting
When the engine coolant temperature is below 40℃, the idle speed should be 1500 r/min, when it is between 40℃ and 70℃, the idle speed should be 1100 r/min, and after reaching 70℃, it should return to normal idle speed. If the engine speed is normal after starting, the coolant temperature sensor should be checked first.
(2) After starting, if the engine speed displayed on the tachometer is lower than the normal idle speed
It may also be due to the sticking of the idle stepper motor in the bypass air passage, which prevents the bypass air passage from opening during starting and warm-up. Remove the corrugated tube (intake hose) between the air filter and throttle, and inspect the throttle. If there is carbon deposition at the throttle, there must also be carbon deposition at the idle stepper motor in the bypass air passage that shares the same working environment. Clean the throttle (fully open) and the idle stepper motor in the bypass air passage with throttle cleaning agent. After cleaning, repeatedly blow with compressed air until it is completely clean, to eliminate the fault.
(3) Place the coolant temperature sensor in a container filled with water and ice. Heat the water in the container, and measure the resistance of the sensor using an ohmmeter at 0°C, 20°C, 80°C, 100°C, and 120°C. Check if the resistance value changes curve matches the manufacturer’s specifications. If the resistance is too high or too low during measurement, or if the characteristic curve of resistance change with temperature does not match the manufacturer’s specifications, the sensor needs to be replaced.
(4) Read the data stream and compare the engine coolant temperature displayed in the data stream with the actual temperature detected by the infrared thermometer. If there is a mismatch, the coolant temperature sensor should be replaced.
Troubleshooting summary of cold car starting difficulty The main reason for difficulty starting a cold car is that the oil pressure in the fuel system cannot be maintained normally or the idle motor is stuck, causing a malfunction.
Therefore, the throttle body and idle motor must be cleaned and maintained regularly. It is generally recommended to clean them every 20,000 kilometers. In special cases such as fuel pump failure, poor fuel quality, or clogged injectors, timely maintenance and cleaning are even more essential. If the vehicle frequently experiences difficulty starting the next day, it is recommended for the owner to have a more detailed inspection of the fuel system at a professional repair shop.
