What are the reasons for difficult cold engine start?

[DiBarrett]

The reasons for difficult cold engine start can be summarized in the following 5 points: 1. Low engine temperature: The temperature inside the engine is insufficient, and both fuel and lubricant temperatures are too low. Therefore, more fuel should be injected during cold starts to meet power requirements. Poor fuel atomization at low temperatures leads to reduced ignition energy, affecting power output and causing the vehicle to shake. 2. Excessive carbon buildup on valves and intake passages causing cold start difficulties: When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold start injector will be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts and making ignition difficult. Only when the carbon deposits become saturated with gasoline will the engine start more easily. After starting, the gasoline adsorbed on the carbon deposits will be drawn into the combustion chamber by the engine's vacuum suction, making the air-fuel mixture too rich. This fluctuation between lean and rich mixtures causes rough idling after a cold start. 3. Faulty coolant temperature sensor: If the engine temperature is -10°C during a cold start but the sensor "tells" the ECU that "the current temperature is 20°C," the ECU will inject fuel based on 20°C conditions, leading to engine shaking. 4. Untimely spark plug replacement: Cold starts require higher ignition energy. After a certain mileage, the electrode gap of spark plugs widens, and when it exceeds the standard, the spark energy generated will significantly weaken, making it unable to properly ignite the air-fuel mixture in the cylinder (commonly known as misfire). 5. Faulty ignition coil: The ignition coil is a transformer responsible for converting the vehicle's low-voltage current into high-voltage electricity, enabling the spark plug to "generate sparks" with sufficient voltage. Once the ignition coil fails, such as due to cracking or leakage, it will result in insufficient or lacking spark plug ignition capability. Consequently, the air-fuel mixture in that cylinder will not combust properly, leading to engine misfire, difficult starts, and acceleration shaking.