An engine operates best with a stoichiometric air-fuel ratio of 14.7:1, ensuring efficient combustion and reduced emissions. When this ratio is disturbed, it results in either a lean or rich mixture. A lean mixture, characterized by excess air, can lead to dangerously high combustion temperatures and knocking, risking damage to components like cylinder walls and pistons. This condition often arises from vacuum leaks or faulty sensors. Conversely, a rich mixture, where fuel exceeds air, can damage the catalytic converter and lead to 'fuel wash,' which strips lubrication from cylinder walls, increasing wear and tear. Additionally, unburnt fuel can dilute engine oil, compromising its effectiveness. The engine control unit (ECU) continuously adjusts fuel input based on oxygen sensor readings to maintain the ideal mixture. However, malfunctioning sensors can mislead the ECU, resulting in improper fuel adjustments and potential engine failure. Understanding these dynamics is essential for effective engine maintenance and longevity.