What Causes a Muffled Engine Sound in Cars?

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Engine sound becoming muffled may be caused by abnormal cylinder operation. Also check the throttle opening to see if there is severe carbon buildup. When noticing a muffled engine sound, you can inspect the following components: 1. Check the fuel supply system - replace the fuel filter and clean the fuel injectors, as these affect the engine's fuel supply requirements. 2. Check the ignition system - examine whether the spark plug gap is too large, which could cause slower spark frequency and affect combustion quality (recommend replacement if needed). 3. Check the intake system - inspect if the air filter is dirty and whether vacuum tubes have aged or leak (clean the throttle body as this affects air intake volume). 4. Check the exhaust system - verify if the catalytic converter is clogged, which impacts exhaust flow (recommend cleaning or replacement). 5. Check whether cylinder compression meets standards (standard compression should be above 8 kg). 6. Verify if the replaced engine oil has the correct viscosity grade - using oil with too high a viscosity grade or overfilling oil can both cause muffled engine sounds.