What Causes the Popping Sound in a Car's Exhaust Pipe?

[Madison]

An abnormal sound from a car's exhaust pipe is caused by an excessively rich air-fuel mixture and faulty valves. The specific reasons are as follows: Excessively Rich Air-Fuel Mixture: When the air-fuel mixture is too rich, incomplete combustion occurs, and the combustion time in the cylinder becomes excessively long. As the engine begins its next power stroke, unburned combustible mixture enters the exhaust pipe along with the exhaust gases. When this mixture encounters fresh air in the exhaust pipe, it reignites, causing engine backfire. At this point, a distinct abnormal sound can be heard from the exhaust pipe. Faulty Valves: If the valves are not sealing properly or do not open sufficiently, the combustion process may be incomplete, preventing the proper expulsion of excess exhaust gases. This can lead to abnormal sounds from the exhaust pipe. However, when the engine speed increases, the relative leakage rate of the valves decreases, and the abnormal sound from the exhaust pipe may disappear as the engine runs smoothly. It is important to note that only severe leakage in the intake valve can cause the cylinder to stop working at low speeds, occasionally accompanied by carburetor backfire during driving.