What Causes Overly Rich Air-Fuel Mixture in Cars?
2 Answers
Reasons for overly rich air-fuel mixture in cars: 1. Idle speed, engine meeting torque requirements leading to overly rich mixture; 2. Oxygen sensor failure; 3. Inaccurate air intake measurement - check for fuel injector leakage and the working performance of the fuel pressure regulator, as poor performance can also cause an overly rich mixture. The air-fuel mixture in cars refers to the combination of fuel and air, typically gasoline, diesel, etc. mixed with air. However, with advancements in automotive technology and fuel diversity, it now also includes mixtures with various combustible gases such as natural gas, methane, coal gas, as well as ethanol, methanol, and other mixtures.
A rich air-fuel mixture is quite common. I've encountered it several times with a few cars I've driven. It mainly happens when there's too little air or too much fuel. For example, if the air filter is clogged or dirty, dust buildup can prevent sufficient air from being drawn in, while the fuel pump keeps sending too much fuel, throwing off the ratio. The fuel injectors could also be problematic—leaking or stuck open, spraying excessive fuel and making the mixture too rich. Faulty sensors, like a bad oxygen sensor or a malfunctioning mass airflow sensor, can mislead the ECU into delivering too much fuel. If the check engine light comes on, take it seriously—don't ignore it. Fixing it early saves trouble; otherwise, the engine loses power, fuel efficiency drops, and you'll feel sluggish performance with black smoke. I recommend checking the air filter annually—keeping it clean helps prevent issues.
