Catalytic Converter – Failure Signs And Testing – Learn The Basics

So, a catalytic converter, is a device used to reduce the emissions, from an internal combustion engine.

Consequently, the catalytic converter works, by breaking down unburned gases, left over by the combustion process. And, requires you to use, unleaded fuel.

This is because the lead in conventional fuels, “poisons” the catalyst, preventing the catalytic converter from working on the pollutants. And, they only work at high temperatures, when the engine has had chance to warm things up.

Above all, without a catalytic converter, your vehicle will no longer be filtering and reducing harmful emissions. Including, hydrocarbons, nitrogen oxides, and carbon monoxide.

Knowing The Basics

The exhaust from the engine gets filtered through this device, so harmful chemicals can be removed like:

• Carbon monoxide (a poisonous gas)
• Nitrogen oxides (a cause of smog and acid rain)
• Hydrocarbons (a cause of smog)

But, a bad (O2) sensor, can feed wrong information to the computer, which can affect the performance of catalytic converter.

Consequently, too rich a fuel mixture, causes unburnt fuel to enter the catalytic converter. Then, at some point it will be damaged, due to thermal shock.

So, inside the converter, the gases flow through a dense honeycomb structure. And, is made from a ceramic and coated with the catalysts. Also, by using a honeycomb structure, the area is greatly increased.

Check Engine Light And Codes

The (CEL) or (MIL), is your best friend, when dealing with emission problems.

So, whenever this light comes on, check for (DTC). The common catalyst failure codes are, P0420 or P0430.

Signs Your Catalytic Converter May Be Failing

The most common signs include:

• Poor acceleration, when stepping on the gas pedal.
• Engine misfiring.
• Noticeably, less fuel efficiency.
• Dark, sooty smoke exiting your exhaust.
• Engine starting trouble.
• Failing an emissions test.
• A pungent sulfuric or rotten egg smell.
• A (CEL), in conjunction with any of these other symptoms.

If the exhaust system is restricted, it may be the result of another underlying problem. The following are the most common causes of catalytic converter failure:

• Poor engine performance or an overly rich air fuel mixture. This can cause the converter to overheat, causing the substrate to melt down. One sign of this is a converter that is red hot. Symptoms include, loss of power at high engine speeds, a hissing noise when accelerating. Also, prolonged cranking, and poor acceleration and fuel economy.
• Leaded fuels can also cause the converter to overheat and the substrate to fail.
• Coolant leaking into the exhaust system or silicone from sealants can coat the catalyst, and render it useless. If the exhaust system has had coolant or silicone contamination. Then, the (O2) sensor and catalyst will have a white coating or glaze that should be visible.

Testing For A Blocked Or Clogged Catalytic Converter

Using A Vacuum Tester

Using A Back Pressure Tester

Just like the vacuum test above, a back pressure test can help you diagnose a clogged exhaust system. This test is done directly at the exhaust system, to detect a clogged catalytic converter or muffler or pipe. This simple test, requires a back pressure gauge.

NOTE: This test is easy to do, as long as you don’t break off a (O2) sensor. (The use of heat or penetrating oil, and a back and forth motion may help, if the threads are rusty).

First, remove the back (O2) sensor. This sensor is usually located directly after the converter.  Most (O2) sensors use an 18mm threaded port. So, one adapter fits many applications. Install the adapter in the (O2) port, and tighten to manufacturer specs.

Then, connect the gauge hose to the adapter. Begin by reading and taking note of the pressure at idle, and at 2500 (RPM). On most vehicles, idle back pressure should not be higher than 1 (PSI). At 2500 (RPM), the reading should not be higher than 3 (PSI). If the readings are high at this point, the blockage probably exists downstream of the test point. And, usually means it is in the muffler or resonator.

If the back pressure is okay at this location, move to the (O2) sensor just ahead of the converter. And, if the back pressure is high at this point, the converter is causing the issue. If the (O2) sensor ahead of the converter tests okay, then the restriction is most likely in the y-pipe. But, there could also be an internal restriction in the air gap pipe. It is located, between the exhaust manifold and the converter.

Checking Temperature With A Infrared Thermometer

Just like the back pressure test above, a temperature test can help you diagnose a clogged exhaust system. This test is done directly at the exhaust system. And, detects a clogged catalytic converter, muffler or pipe. This simple test, requires a infrared thermometer.

In a good catalytic converter, the rear of the converter will be, 20 degrees hotter than the front.

The best way to do a temperature check, is by using an infrared thermometer. Here are the steps:

1. Switch on the engine and let it idle for 20 minutes. This allows it to rise to its normal temperature. You can also take the car for a short drive on the road or highway then come back.
2. Leave the engine idling and set the car in park. (or neutral for a manual)
3. Check if you have enough clearance to get under the car. If you don’t, raise the front of the car and support it on jack stands. The catalytic converter is usually located close to the engine, so you only need to raise the front. Place blocks against the rear wheels for added safety.

4. A infrared thermometer is a must.

5. Take an infrared thermometer and measure the temperature at the front of the catalytic converter. You only need to measure the surface temperature, so an infrared thermometer is perfect. It also allows you to maintain a safe distance from the hot converter.
6. Make sure you hold the infrared thermometer at the right distance, from the point whose temperature you are taking. A distance of about 12 cm away from the surface of the converter, will give you an accurate reading.
7. Record the front reading then measure the temperature at the rear of the converter and record it as well.

Comparing the two readings will tell you whether your car’s catalytic converter is working as expected.

If the front and rear readings are similar or almost the same, there’s a problem. And, if the front temperature is higher than the rear temperature, there’s a problem.

But, if the rear temperature of the catalytic converter is 20 or more degrees hotter than the front. Then, your catalytic converter is likely okay. If you are still experiencing problems with the engine and exhaust, check the muffler.

A working catalytic converter will have hotter gasses coming out at the rear, compared to the exhaust gasses coming in.

If you get a lower rear temperature, it’s likely that the catalyst inside has deteriorated. And, is not converting exhaust gasses or it is clogged up.

Using A Pressure Transducer

Just like the temperature test above, a back pressure test can help you diagnose a clogged exhaust system. This test is done directly at a cylinder, to detect a clogged catalytic converter or muffler or pipe. This simple test, requires a pressure transducer.

This is where for some it gets a little tricky. Unless you have some experience at reading waveforms, it might be best to watch a video. There are tons out there. Good luck!

Knowing The Basics