What Causes a Car to Stall When Hot but Start When Cold?
2 Answers
The reasons why a car stalls when hot but can start when cold are as follows: 1. Carbon deposits. At high temperatures, carbon deposits have a strong adsorption effect on gasoline. If there are excessive carbon deposits on components like the intake valve, they can adsorb some fuel, leading to an overly lean air-fuel mixture, which affects starting. 2. The coolant temperature sensor plays a role in adjusting the fuel injection pulse width. If it malfunctions and fails to provide the correct temperature signal, it can affect fuel injection, leading to an abnormal air-fuel ratio and difficulty in starting. 3. The intake air temperature sensor is similar to the coolant temperature sensor and is also used to adjust fuel injection. A higher intake air temperature sensor reading can result in a richer air-fuel mixture, while a faulty or poorly grounded intake air temperature sensor can cause an overly lean mixture. 4. Fuel quality issues. After the car stalls when hot, the engine compartment remains at a high temperature. If the fuel is prone to evaporation, it can create high vapor pressure in the fuel rail. When this pressure exceeds the fuel system's pressure, it can cause vapor lock, leading to overly lean fuel vapor injection and difficulty in starting.
After driving for so many years, I've found that a car that stalls when hot but starts when cold most commonly has an ignition system issue. When the engine is hot, the ignition coil can fail due to high temperatures, leading to insufficient ignition energy. Spark plugs that are worn or have incorrect gaps often fail to ignite at high temperatures. The fuel pump, which operates inside the fuel tank, may also struggle to supply fuel properly when the fuel temperature is too high, or even experience vapor lock. Sensor failures shouldn't be overlooked either—for example, an inaccurate coolant temperature sensor signal can cause the ECU to miscalculate, leading to improper fuel injection. Additionally, severe carbon buildup in hot engine conditions can absorb fuel, causing the air-fuel mixture to become too lean and stall. For these issues, it's best to consult a professional repair shop rather than attempting DIY fixes.
