Catalytic Converter Testing

The early catalytic converters, known as two-way converters, primarily targeted HC and CO reduction using noble metals like platinum and palladium. However, their limitations became apparent as environmental regulations tightened. Automakers were mandated to develop converters capable of reducing not just HC and CO, but also nitrogen oxides (NOX). Enter the dual-bed converter, which introduced a new noble metal, rhodium, to reduce NOX. In a CO-rich environment, rhodium facilitated the removal of oxygen from NOX, reverting it to nitrogen (N2) and oxygen (O2).

The combustion process in internal combustion engines inherently produces pollutants, with nitrogen oxides (NOX) being one of the most harmful. NOX formation occurs when combustion chamber temperatures exceed 2500 degrees Fahrenheit. Under normal conditions, nitrogen remains inert, but it combines with oxygen at higher temperatures to form NOX.

Dual-bed converters comprised two compartments: a reduction bed positioned upstream and an oxidizing bed downstream. Oxygen was injected into the oxidizing bed to convert HC and CO to H2O and CO2. The remaining oxygen in the front bed was a byproduct of the combustion process.

Subsequent advancements led to the development of three-way catalytic converters, representing a new generation of emission control technology. These converters possess the unique ability to reduce and oxidize pollutants simultaneously. Constructed with a ceramic honeycomb mesh coated with alumina, they incorporate noble metals such as platinum, palladium, rhodium, and a newcomer, cerium.

Cerium plays a crucial role by storing oxygen in lean mixtures and releasing it in rich mixtures, ensuring continuous oxidation. This converter's effectiveness relies on a feedback loop facilitated by onboard computer systems. An oxygen sensor monitors the exhaust gases, allowing the engine control unit to adjust the fuel mixture accordingly, maintaining optimal conditions for catalytic conversion.

In summary, the evolution of catalytic converters—from two-way to dual-bed to three-way—mirrors the automotive industry's commitment to environmental stewardship. These advancements reduce emissions and underscore the synergy between technological innovation and regulatory compliance, paving the way for cleaner and more sustainable transportation solutions.

To assess the efficiency of a catalytic converter accurately, a method involving drilling small access holes in the exhaust system, both before and after the converter, is employed. This technique allows for sampling exhaust gases using a specialized analyzer probe.

Before initiating this procedure, ensuring the exhaust system is in good condition is crucial. Attempting to drill into or weld a corroded exhaust system poses risks and may lead to further complications, testing the patience of even the most experienced technicians.

The analysis compares the emissions readings taken before and after the catalytic converter. Ideally, emissions levels should significantly reduce by at least 50% to 60% after passing through the converter. This method provides the most precise assessment of the converter's efficiency, particularly in reducing harmful nitrogen oxide (NOx) emissions.

Despite its effectiveness, this testing procedure carries inherent risks. Intrusive tests like this may result in customer disputes, especially if the exhaust system sustains damage during the process and cannot be adequately repaired afterward.

It's worth noting that catalytic converters play a crucial role in reducing NOx emissions. At Smog Fix, we have observed converters capable of reducing NOx levels by as much as 1500 parts per million (PPM). However, conducting this intrusive test remains challenging and requires careful consideration of potential repercussions.

One potential solution to mitigate these challenges would be for automakers to include pre-catalyst access points in exhaust systems. Such provisions could streamline testing processes while minimizing the risks associated with intrusive procedures.

In conclusion, while the access hole method offers unparalleled insights into catalytic converter efficiency, it necessitates careful execution and consideration of potential consequences. As automotive technology continues to evolve, collaborative efforts between manufacturers and service providers are essential to address these challenges effectively.

This procedure tests the efficiency of a catalytic converter in reducing hydrocarbon (HC) emissions. Here's a simplified breakdown:

1. Start the vehicle and run it until the catalytic converter is hot.

2. Turn off the engine for three minutes.

3. Ground one spark plug wire and restart the engine, causing a misfire and increasing HC emissions.

4. Monitor HC levels using a gas analyzer, recording the highest level observed.

5. The HC level should start to decrease, but this condition shouldn't continue for more than two minutes.

6. Record the peak HC level and the final HC level after the reduction.

7. Subtract the lowest HC reading from the highest to determine the reduction achieved by the converter.

8. Divide this reduction by the highest-level reading to calculate the percentage of reduction achieved.

9. A minimum reduction of 35% is expected. If reduction is low, the converter may be unable to reduce HC emissions effectively.

Example:

• Highest-level HC = 945PPM

• Final level HC = 355PPM

• Reduction = 945PPM - 355PPM = 590PPM

• Percentage reduction = (590 / 945) x 100 = 62%

This test evaluates the converter's ability to oxidize excessive HC emissions a misfire produces. When the engine starts, it reaches a temperature where the converter can begin oxidizing emissions. After shutting off the engine briefly and restarting it, the converter is cooler and doesn't oxidize immediately, causing HC levels to rise. Once the converter reaches its optimal temperature, it oxidizes HC to water and carbon dioxide.

Some converters achieve 100% reduction; newer ones perform well on this test. However, a good converter can make even a poorly running engine appear clean in tailpipe emissions tests.

This test is designed for cars equipped with an OBDII fuel metering system. Follow these steps:

1. Ensure the car is at normal operating temperature.

2. You'll need a DSO (digital storage oscilloscope) for this test.

3. Set up the DSO in dual trace mode and connect the leads parallel to the front and rear oxygen (O2) sensor output wires.

4. Start the engine and observe the voltage readings. The front O2 sensor voltage should fluctuate, while the rear O2 sensor voltage will be more stable.

5. Disconnecting a large intake vacuum hose creates a lean condition. The voltages of the front and rear O2 sensors should drop to around 0.2 volts.

6. Reattach the vacuum hose. The mixture will immediately become rich, causing the front O2 sensor voltage to rise instantly, but there will be over a 2-second delay before the rear O2 sensor voltage increases.

7. The rear O2 sensor response delay is due to noble metal (cerium) in the catalytic converter, which stores oxygen during lean conditions and releases it during rich conditions.

8. This test assesses the catalytic converter's ability to store and release oxygen using cerium. If the converter fails this test, it suggests a weakness in its oxygen storage capability.

9. The purpose of the O2 sensor is to inform the PCM (powertrain control module) about the mixture's richness or leanness, allowing the PCM to adjust the mixture accordingly for efficient catalytic converter operation.

10. Oxidizing and reducing refer to adding or removing oxygen in the catalytic converter's reactions.

11. This test alone isn't sufficient to determine catalytic converter efficiency, but when combined with other tests, it helps decide whether replacement is necessary.

The engine must be warmed to its usual temperature before conducting this test. First, ensure the catalytic converter is hot by running the engine at 2500 rpm for two minutes. Then, stop the engine and disable the ignition. Crank the engine for about 10 seconds while observing the 5-gas analyzer. The CO2 level should reach at least 12.5% by the end of the cranking period, and the HC level should not exceed 500 PPM. It's common for HC readings to be above 500 PPM in this test, so don't be too critical of this result.

Propane should be added to the air intake system for vehicles with carburetors. However, propane is unnecessary for fuel-injected vehicles unless the fuel has been disabled with the ignition.

The purpose of this test is to check if the catalytic converter can convert HC (hydrocarbons) into CO2 (carbon dioxide) and H2O (water). Think of the catalytic converter as a combustion chamber requiring heat, air, and fuel. When the converter is heated up and the engine is cranked with the ignition disabled, air and fuel enter the catalytic converter, initiating the burning process. Consequently, HC is converted into CO2 and H2O. This test is quick, easy, and provides fairly consistent results on the efficiency of the catalytic converter.

The traditional method of testing catalytic converter efficiency involves measuring the temperature of the exhaust before and after it passes through the converter. A temperature increase of around 150° to 300° Fahrenheit after passing through the converter suggests effective oxidation of pollutants. However, this method is less reliable for newer three-way converters as they also reduce pollutants, which can lower the temperature inside the converter. In excessive NOX emissions, the reduction process can significantly decrease the converter's temperature. Introducing a misfire by disconnecting a spark plug wire can increase hydrocarbon (HC) emissions, causing the converter to heat up as it works to oxidize the excess HC.

To test the efficiency of a vehicle's catalytic converter, follow these steps:

1. Use a four or five-gas analyzer to probe the tailpipe when the vehicle is at average operating temperature.

2. Run the engine at 2200 RPM and monitor the CO (carbon monoxide) and O2 (oxygen) readings.

3. If the CO level drops to zero and the O2 level is above 0.5%, add propane until the CO level reaches 0.5%.

4. Perform a snap acceleration of the engine.

5. When the CO peaks during acceleration, the O2 should not exceed 1.2% above its level before acceleration.

6. This test assesses the catalytic converter's ability to utilize oxygen generated during throttle snapping to oxidize CO produced by sudden acceleration.

7. Throttle snapping causes the PCM (Powertrain Control Module) or carburetor to lean the mixture during deceleration, creating a specific environment for testing the catalytic converter's efficiency.

8. The converter oxidizes excess CO using the extra oxygen, converting it into CO2.

9. This test provides a quick and easy way to determine if the catalytic converter can convert CO into CO2 effectively.