What are the causes of an excessively lean air-fuel mixture in an engine?
2 Answers
An excessively lean air-fuel mixture is primarily caused by insufficient fuel injection: 1. Various intake sensors fail to accurately detect the intake air volume, resulting in insufficient fuel injection. 2. Excessive carbon deposits absorb the injected fuel. 3. The closed-loop control of the oxygen sensor fails. Effects of an excessively lean air-fuel mixture in an engine: 1. When the mixture is too lean, the combustion speed of the fuel decreases, and part of the mixture combustion occurs as the piston moves toward the bottom dead center. 2. In severe cases, the combustion process may even be delayed until after the start of the next cycle's intake stroke, causing the residual flame in the cylinder to ignite the mixture in the intake pipe through the open intake valve, leading to backfire and knocking noises, accompanied by popping sounds in the exhaust pipe. 3. The combustion of this part of the mixture not only converts less heat into mechanical work but also increases the heat lost through the cylinder wall to the coolant or cooling fins. Therefore, an excessively lean mixture can cause engine overheating and reduced power output. 4. An excessively lean mixture can lead to higher idle speeds, and when accelerating and releasing the throttle, the engine speed may take a longer time to drop back to idle. In such cases, removing the spark plugs will reveal white-colored electrodes, confirming that the combustible mixture is too lean.
As someone who drives frequently, I've found that a lean fuel mixture is mainly caused by too much air or too little gasoline. The most common issue is air leaks in the intake system, such as cracked old rubber hoses or gaskets, which allow extra air to be sucked in. Another cause is clogged or carbon-fouled fuel injectors that can't spray enough fuel, or low fuel pressure leading to inadequate fuel delivery. These problems can result in severe engine shaking, poor acceleration, and easier stalling when the engine is warm. Over time, engine overheating can shorten its lifespan and cause emissions to fail standards. I remember seeing many cases when I worked in auto repair, all due to owners neglecting basic maintenance. So, I recommend regularly checking the intake system's sealing and injector conditions. Don't delay addressing issues—don't let small problems ruin major components.
