What Causes Low Efficiency in Three-Way Catalytic Converters?

[EllianaAnn]

Low efficiency in three-way catalytic converters is due to blockages in the system. When blocked, the vehicle's exhaust flow becomes restricted, affecting performance and increasing fuel consumption. In such cases, it's essential to determine the severity of the blockage. For mild to moderate blockages, specialized machines designed to oxidize and clean the three-way catalytic converter can be used for repair. However, severe blockages require immediate replacement of the converter. Ignoring low efficiency can render the three-way catalytic converter non-functional, leading to excessive exhaust emissions. The primary causes of reduced efficiency are aging or clogging of the converter, which not only significantly increases fuel consumption and reduces power but also results in excessive emissions. In severe cases, the exhaust pipe may overheat and turn red, posing a risk of vehicle fire. Working Principle of Three-Way Catalytic Converters: When engine exhaust passes through the exhaust pipe, the catalytic agents in the three-way catalytic converter enhance the activity of CO, HC, and NOx, facilitating oxidation-reduction reactions. CO is oxidized into colorless, non-toxic CO2 at high temperatures, HC compounds are oxidized into H2O and CO2, and NOx is reduced into N2 (nitrogen) and O2 (oxygen). This process effectively purifies the engine's exhaust emissions.

[AlexanderFitz]

I failed my last emissions test because the three-way catalytic converter was inefficient. The mechanic said the main reasons were: the car is often driven short distances, so the catalytic converter doesn't reach operating temperature before shutting down, and carbon deposits clog the honeycomb structure. There's also an oil burning issue, where oil ash blocks the catalytic channels. Additionally, using substandard gasoline from small gas stations can cause sulfur and lead to poison and deactivate the catalyst. Long-term use of low-quality oil with metal additives can also deposit on the carrier. The car's undercarriage was scraped and not repaired in time, possibly cracking the ceramic carrier of the catalytic converter. Finally, a faulty oxygen sensor can disrupt the air-fuel ratio, causing the catalytic converter to stop working entirely. It's recommended to occasionally drive on the highway, use fuel system cleaner, and perform deep maintenance every 80,000 kilometers.

[Peter]

As a car owner who frequently visits repair shops, I've found that most issues with the catalytic converter stem from these five aspects: Firstly, poor fuel quality with excessive sulfur content causing chemical poisoning; secondly, engine oil burning, especially in older cars with worn piston rings, where oil ash clogs the catalytic pores; thirdly, abnormal ignition systems, such as aged spark plugs leading to incomplete combustion of the air-fuel mixture, allowing unburned gasoline to enter the converter and damage the substrate; fourthly, undercarriage impacts causing the ceramic substrate to crack; and finally, frequent short-distance driving preventing the converter from reaching its optimal operating temperature of 300°C, leading to carbon buildup clogging the honeycomb structure. Regularly checking the oxygen sensor data stream can help detect problems early.

[StDawson]

From a technical perspective, the core issue of catalytic efficiency decline lies in the deactivation of active materials. Thermal deactivation is the most common, such as misfires causing unburned mixture to undergo secondary combustion in the catalyst, where temperatures up to 1200°C can lead to sintering and agglomeration of precious metals. Chemical poisoning occurs in three forms: leaded gasoline coats platinum, palladium, and rhodium active sites with lead compounds; phosphorus and zinc originate from oil additives; and sulfides temporarily poison the catalyst. Mechanical blockage is another factor: carbon deposits clog the carrier channels, and broken ceramic carriers increase exhaust backpressure. Additionally, the ECU incorrectly adjusts the air-fuel ratio based on signals from failed oxygen sensors, creating a vicious cycle. Maintaining precise air-fuel ratios and avoiding high temperatures are key.

[VonMaria]

From an environmental perspective, a failed catalytic converter isn't just a car issue. Using gasoline with manganese-based anti-knock additives (MMT) forms brown deposits. During prolonged low-speed driving, carbon buildup absorbs HC compounds, directly emitting pollutants during cold starts. Coolant leakage into the exhaust system contaminates catalyst coatings with ethylene glycol. Aftermarket straight-pipe headers cause insufficient temperatures. More critically, maintenance awareness: many ignore the recommendation to replace oxygen sensors every 100,000 km. Aged oxygen sensors can deviate by ±15%, keeping the converter in sustained suboptimal conditions. We recommend diagnosing replacement needs by combining P0420 trouble codes with abnormal exhaust sounds.