Mechanics

Plugged Catalytic Converter Test

The catalytic converter on your vehicle is an emissions component that is designed to eliminate pollutants that are left over from combustion. Pollutants such as Nitrogen Oxides, (Nox), Hydrocarbons, (HC), and Carbon Monoxide, (CO), are reduced to extremely low levels as they pass through the converter‘s honeycomb inside. Thus, it reduces the harmful pollutants from entering the atmosphere. A faulty converter will usually cause a rough engine idle, poor fuel mileage, and a loss of power at higher speeds. 

When the vehicle is operating properly, the converter is able to function with little effort. However, excessive oil consumption, poor or weak ignition (fouled spark plugs), a burnt or leaking exhaust valve, a faulty oxygen sensor, excessive fuel pressure, low engine compression, and other items can cause the converter to fail. Please keep in mind, a converter can fail without being plugged and they can be easily checked. A plugged converter, usually caused by overheating, and can be accompanied by loss of engine power output.

The catalytic converter has a large temperature range of operation. Most will not begin to operate until they reach between 400 to 600 degrees Fahrenheit. From there, normal operation can be upwards of 1,600 degrees Fahrenheit. The higher the temperature goes is usually the result of additional pollutants in the exhaust. If the engine is running poorly enough and the converter’s temperature soars much higher, it can cause the internal honeycomb itself to begin to melt and create a partially or totally plugged converter. 

A simple test for this is to simply drive the vehicle until it is at normal operating temperature and inspect the converter. Often times they become so hot, they glow red. Also, the insides can become loose, identified by a rattle, and can cause a partial blockage. Before we start park your car on a smooth flat surface with the emergency brake on, while the car is in park. The engine will need to be at operating temperature so wear gloves, protective clothing and eyewear.
 

How to Test a Catalytic Converter Efficiency

Tools and Supplies Needed to Complete this Test

1. Temperature probe - Infrared IR Meter

2. Creeper (A low flat board with wheels used to lay on to get under the car with.)

3. Flashlight
 

Instructions

Step 1 - After driving the car for at least 15 minuets park the vehicle on a level surface, apply the parking brake, start the engine, and allow it idle.

Step 2 - Using a temperature probe (infrared meter), check the difference in exhaust temperature at both the inlet and outlet of the converter. The temperature exiting the converter should be around 30 to 100 degrees Fahrenheit hotter. On older vehicles with carburetor, the temperature difference will be closer to 100 degrees Fahrenheit.

Step 3 - If the temperature doesn’t change, the converter could be bad inside. To check, shut off the engine and allow the exhaust to cool. Once cooled remove the catalytic convert and inspect. If the honey comb is broken out the converter has failed and needs replacing.


How to Test for a Plugged Catalytic Converter

Tools and Supplies Needed to Complete this Job

1. Vacuum gauge

2. Flashlight

3. Needle Nose Pliers
 

Instructions

Step 1 - Attach a vacuum gauge to a vacuum port on the intake.

Step 2 - Start the engine and check the intake vacuum. That is your baseline. Normal pressure should be between 15 and 22 inches of vacuum.

Step 3 - Rev the engine to 2,500 RPM’s. There should be a brief time that the pressure drops, but it should return to nearly the baseline pressure you had at idle within a few seconds.

Step 4 - Keep the engine at 2,500 RPM’s and watch the vacuum gauge. If it is low or continues to drop, that is a good indication that there is a blockage in the exhaust system causing back pressure to build. The most likely problem is the converter.
 

Best Practices

It is important to mention that a faulty converter is usually caused by something other than the converter itself. Therefore, it is important to determine what caused the problem. Otherwise, you will be replacing a new converter soon after it is installed. By J. Feliciani / AKA Jacobandnickolas.

The exhaust system in your vehicle is designed to release exhaust gases from the engine to the rear of the car. This system is designed to have about 3 pounds of exhaust backpressure under heavy throttle. This means the engine should not have to push more than 3 pounds of pressure to release the exhaust at any given time. If a catalytic converter plugs or breaks apart it will plug the exhaust system causing engine surging, low power and stalling. Because of the extreme temperatures the catalytic converter produces the catalyst material can crack and break apart clogging the outlet port of the converter causing low power and stalling.

AUTHOR


Written by
Co-Founder and CEO of 2CarPros.com
35 years in the automotive repair field, ASE Master Technician, Advanced Electrical and Mechanical Theory.


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Article first published (Updated 2013-09-16)