What causes a car engine to sound muffled and not crisp?

[OAyla]

The reasons for a car engine sounding muffled and not crisp include insufficient engine power and damaged spark plugs. Details are as follows: Insufficient engine power: A muffled and not crisp sound from the car engine indicates insufficient engine power, often noticeable during high-speed driving or uphill, especially under heavy loads. The engine clearly lacks power, and when accelerating by pressing the throttle, the speed does not increase rapidly. The exhaust feels sluggish, the driving lacks strength, and fuel consumption rises sharply. Damaged spark plugs: Check the power supply system to see if the spark plug's ignition head is too large, causing slow spark frequency and affecting the engine's combustion quality. It is recommended to replace them.

[MilaLynn]

I encountered a similar situation just last week, and the car felt particularly sluggish. The main culprit was carbon buildup—there was a thick layer of sludge on the piston tops and throttle body, preventing the gasoline from burning completely and stifling the power. The spark plugs were also suspect; when I took them out, the center electrodes were worn down, and the sparking sounded weak and inconsistent. Don’t forget to check the air filter too—I skipped replacing it during the last maintenance, and it got so clogged that the engine struggled to breathe, like it was wearing a mask. A blocked exhaust pipe is even worse; once, a plastic bag got stuck in mine, and the sound was muffled like a drum. If all else fails, check the cylinder compression—leaky cylinders make the most unpleasant noise. My advice: start by cleaning the throttle body and replacing the spark plugs. That should solve 70–80% of the problem.

[Thalia]

In recent years, I've frequently encountered the issue of a sluggish engine when repairing cars. The top culprit is poor fuel quality—substandard 92-octane gasoline from small gas stations often contains excessive water, causing knocking sounds and a dull, sloshing noise during combustion. Aging ignition coils are also common, leading to misfires across cylinders one by one, making the car shudder and the sound turn muffled. Degraded engine oil is particularly easy to overlook; oil unchanged for half a year thickens like porridge, forcing engine components to labor harder, naturally resulting in a sluggish noise. I’ve encountered exhaust leaks a few times—rusted-through tailpipes produce a puffing leakage sound. The most troublesome issue is a faulty oxygen sensor, where the ECU misfires fuel, causing incomplete combustion. Always read the trouble codes first, focusing on the voltage readings of the upstream O2 sensor—if this part fails, the whole car loses its vigor.

[DelMarley]

Abnormal engine noise is mostly a maintenance issue. I make it a habit to clean the fuel injectors every 5,000 kilometers—when dirty, they spray droplets instead of mist, causing a sputtering sound during combustion rather than a crisp one. Spark plugs must be replaced every 20,000 kilometers; old ones cause delayed ignition, making the ticking sound duller. Last time, a clogged air filter cost me dearly—insufficient airflow made the cylinders feel oxygen-starved. Using the wrong oil grade is the worst; putting 5W40 oil in a car that requires 0W20 makes the engine so sluggish it "sings off-key." Also, pay attention to gas stations—95-octane fuel indeed burns more completely than 92. I recommend a monthly high-RPM run to reduce carbon buildup, keeping the engine sound naturally clear.