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A Guide To Catalytic Converters

What is a Catalytic Converter?

A catalytic converter is a device used to reduce the emissions from an internal combustion engine (used in most modern day automobiles and vehicles). Not enough oxygen is available to oxidize the carbon fuel in these engines completely into carbon dioxide and water; thus toxic by-products are produced. Catalytic converters are used in exhaust systems to provide a site for the oxidationand reduction of toxic by-products (like nitrogen oxides, carbon monoxide, and hydrocarbons) of fuel into less hazardous substances such as carbon dioxide, water vapor, and nitrogen gas.

What does a Catalytic Converter do?

A catalytic converter is a device that uses a catalyst to convert three harmful compounds in car exhaust into harmless compounds.

The three harmful compounds are:
-Hydrocarbons (in the form of unburned gasoline)
-Carbon monoxide (formed by the combustion of gasoline)
-Nitrogen oxides (created when the heat in the engine forces nitrogen in the air to combine with oxygen)

Carbon monoxide is a poison for any air-breathing animal. Nitrogen oxides lead to smog and acid rain, and hydrocarbonsproduce smog.

In a catalytic converter, the catalyst (in the form of platinum and palladium) is coated onto a ceramic honeycomb or ceramic beads that are housed in a muffler-like package attached to the exhaust pipe. The catalyst helps to convert carbon monoxide into carbon dioxide. It converts the hydrocarbons into carbon dioxide and water. It also converts the nitrogen oxides back into nitrogen and oxygen.


Why do Catalytic Converters Fail?


Any malfunction causing an unusually high level of HC or CO (in conjunction with high levels of O2) to enter the converter, will dramatically elevate its temperature. 
Potential causes for high HC readings may include:Misfires
AFR Cylinder imbalance
Excessive engine or vehicle load 
   - Fuel delivery system or fuel quality 
   - Sluggish (worn out) O2 sensors 
   - Excessive backpressure 
   - Low compression
Poor spark, or weak ignition
NOTE: Temperatures in excess of 1600º F may damage catalyst, without visible signs of melting.


Catalyst poisoning occurs when the converter is exposed to emissions containing substances that coat the working surfaces, enveloping the catalyst to the point it cannot contact - and treat - the exhaust. 
Potential causes for coated or fouled substrate may include:Excessive carbon build-up in exhaust
Internal coolant leaks (head / intake gasket)
Use of non-converter-safe gasket sealants
Excessive oil consumption (burning oil)
Improper fuels or additives (E85, diesel)


The primary cause of structural damage is road debris striking the converter. Normally, some evidence of impact is visible on the converter shield. 
Other conditions that may cause structural damage:Corrosion
Thermal shock
Metal fatigue
Stress fractures
Stripped O2 Sensor threads
Flex pipe failure
Air-gap pipe failure


Symptoms of Catalytic Converter Failure

If you suspect you have a failing catalytic converter it is advisable to take the car to your mechanic and have them diagnose the problem. A catalytic converter is a vital part of the vehicle exhaust system. It works to convert harm­ful gasses in exhaust systems and change them into safe compounds that can be emitted into the atmosphere and cause less damage to the environment. The catalytic converter is placed between the engine and the exhaust muffler on the underside of the car. It is not common for a catalytic converter to fail. They are usually more subject to external damage like impact from debris or internal engine damage cause by overheating.

  • Misfiring

Misfiring in the engine system can cause the catalyst to over heat. Alternatively, an exceptionally rich fuel mixture will exhibit similar symptoms. When there is a presence of an extra rich fuel mixture raw fuel enters the catalytic converter and is ignited. This can cause the catalyst components to melt under such conditions.

  • Check Performance

Exhaust becomes trapped in front of the catalyst and there is a latent reduction in performance. This is created by back pressure which affects the running of your engine and stops it breathing. The sudden increase in back pressure can cause your engine to stall during your drive. It will act as though there is an air lock in your system. It will cause the car jerk or feel like there is no fuel reaching the engine when you push the accelerator.

  • Check Fuel Economy

You will most certainly become aware of deterioration in the economy of your fuel. Your car will utilize a noticeable amount more gas than usual and this will cost you significantly if the only fault is caused by a failing converter.

  • Check the Exhaust System

Assessing the cause of a failing catalytic converter can sometimes be traced back to an error in the fuel system. A distinctive sign of this is a restriction in the performance of the exhaust system. It is indicative of the melting of catalyst materials inside. 

  • Test the Carburetor

If your vehicle is equipped with a carburetor and you know how to test the catalytic converter, then test it. Remove the air cleaner and enlist the help of a friend. The will need to hold a strong light near the carburetor intake. Glance over the top of the carburetor toward where the light is shining and rev the engine. If you notice signs of fuel vapor suspended over the carburetor, you will be able to safely deduce that there is a clog in the catalytic converter.

  • Oxygen

Another way to identify whether a catalytic converter is failing is to temporarily take out the oxygen sensors from the exhaust. If there is an obvious alteration in the performance of the vehicle then you can be sure the converter has clog and is failing.

  • Alien Chemicals in the Converter

Contamination of the chemical mechanisms inside the catalytic converter, caused by the addition of substances such as motor oil or antifreeze can prevent the converter from performing correctly. You will notice a raised level of carbon emissions from the converter if this happens and you will need to replace the converter before it does damage to your entire exhaust system or emits an illegal amount of emissions into the atmosphere.

What is OBD-II?

On-Board Diagnostics (OBD) refers to the vehicles self diagnostic system. The system was developed to help motorist and service technicians diagnose and service vehicles computerized engine management systems, as well as to inform the motorist when a potential problem exists regarding the emissions control systems of the vehicle. Αt the beginning with the 1996 model year, a new system was develope. The new system known as OBDII requires all light duty cars and trucks to monitor specific systems using generic criteria for evaluation and reporting of system status, and for indicating problems to the motorist and/or technician.

The Engine Control Module (ECM) or Powertrain Control Module (PCM) continuously monitors the engine for conditions that can cause an increase on tailpipe emissions. If the ECM or PCM detects a potential problem with the engine, a warning light called a "malfunction indicator light" (MIL) on the dashboard is illuminated to alert the driver of a problem. This light is usually identified by the words "Check Engine," "Service Engine Soon," or the word "Check" along with an engine symbol. The ECM or PCM will also stored a Diagnostic Trouble Code" (DTC) in the computer's memory. This DTC can be retrieved with a code reader device to help diagnose problems with the vehicle.

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