What Causes Evaporative Emission System Leaks?
3 Answers
Here are the specific causes of evaporative emission system leaks: 1. Poor sealing: The fuel tank cap gasket is faulty, or the sealing at pipe connections is inadequate, leading to leaks. 2. Poor contact: Poor welding at the carbon canister friction weld or loose seals at the carbon canister engine solenoid valve or carbon canister atmospheric vent solenoid valve. 3. Punctures creating leak points: Pipes, carbon canister, or fuel tank punctured by gravel, causing leaks. Below is additional information about the evaporative emission system: 1. Impact of leaks: If the evaporative emission system has leaks, gasoline can easily evaporate, and fuel vapors will escape from the fuel tank. If these vapors are not controlled, they not only pollute the atmosphere but also waste energy. 2. Malfunction indicator lamp (MIL): China VI vehicles require the OBD system to detect evaporative emission system leaks. If the leak exceeds the equivalent of a 1mm (0.04-inch) diameter hole, the OBD must illuminate the MIL.
There are quite a few reasons for evaporative emission system leaks. When working on cars, I often see aging or deformed fuel tank cap seals causing poor sealing, allowing vapors to escape. Loose or cracked connections in the tubing, especially in older vehicles where plastic pipes become brittle and prone to cracking over time, can be culprits. A saturated or internally damaged charcoal canister that can't absorb fuel vapors, or stuck/damaged valves with poor sealing can also cause leaks. Additionally, overfilling the tank during refueling may allow liquid fuel to enter the system, blocking pipes and increasing pressure leading to leaks. Lack of regular vehicle maintenance or improper repairs after accidents in these areas may cause issues. Leaks not only affect fuel consumption but may also trigger the check engine light, and are environmentally unfriendly. It's recommended to inspect these components during every maintenance service.
I've been driving an old car for over a decade, and most evaporation leaks I've encountered were due to either a loose fuel tank cap or a worn-out sealing ring causing air leaks. There are also those thin pipe connections that come loose or get rusted through. The charcoal canister, when used for a long time, can fill up its adsorption capacity and start leaking vapor. Faulty or stuck control valves may also fail to seal properly. The system is originally designed to prevent gasoline fumes from escaping, and leaks often result in fuel odors inside the car or even dashboard warning lights. In daily use, avoiding overfilling the tank and regularly replacing the air filter can help reduce risks. If problems arise, it's best to take it to a professional repair shop immediately rather than delaying.
