Why does the car fail to start when hot but starts after cooling down?

[Karl]

There are several specific reasons why a car may fail to start when hot but starts after cooling down: 1. Fuel injector leakage: While fuel injection is normal operation, leakage constitutes additional fuel supply. The more severe the injector leakage, the richer the air-fuel mixture becomes, making it difficult to start when hot. 2. Damaged carbon canister purge valve: During hot starts, fuel atomization is normally sufficient without additional vapor supply. If the carbon canister continues supplying vapor to the intake, it creates an overly rich mixture, leading to starting difficulties. 3. Fuel quality: After hot shutdown, the engine compartment remains quite warm. If the fuel is highly volatile, it can form excessive vapor pressure in the fuel rail. When this pressure exceeds the fuel system pressure, vapor lock occurs, causing the injectors to deliver overly lean fuel vapor, resulting in starting problems.