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I hope the following information will be useful for all Mazda6s owners.

CATALYTIC CONVERTER FAILURES:

If a catalytic converter needs replacing, one of the problems below most likely contributed to its failure.

Engine Tune-Up Required.
A number of problems could occur to the catalytic converter as the result of an engine that is out of tune. Any time an engine is operating outside proper specifications, unnecessary wear and damage may be caused to the catalytic converter as well as the engine itself. The damage is often the result of an incorrect air/fuel mixture, incorrect timing, or misfiring spark plugs. Any of these conditions could lead to catalytic converter failure or worse.
Excess Fuel Entering Exhaust.
The fuel that powers your vehicle is meant to burn in the combustion chamber only. Any fuel that leaves the combustion chamber unburned will enter the exhaust system and light-off when it reaches the catalytic converter. This can super-heat the converter far above normal operating conditions and cause a meltdown. Possible causes are an incorrect fuel mixture, incorrect timing, corroded spark plugs, a faulty oxygen sensor, sticking float, faulty fuel injector or a malfunctioning check valve.
Oil or Antifreeze Entering Exhaust.
Oil or antifreeze entering the exhaust system can block the air passages by creating a heavy carbon soot that coats the ceramic catalyst. These heavy carbon deposits create two problems. First, the carbon deposits prevent the catalytic converter from reducing harmful emission in the exhaust flow. And second, the carbon deposits clog the pores in the ceramic catalyst and block exhaust flow, increasing backpressure and causing heat and exhaust to back up into the engine compartment. Your engine may actually draw burnt exhaust gasses back into the combustion chamber and dilute the efficiency of the next burn cycle. The result is a loss of power and overheated engine components. Possible causes are worn piston rings, faulty valve seals, failed gaskets or warped engine components.
Deteriorated Spark Plug or Spark Plug Wires.
Spark plugs that don’t fire, or misfire, cause unburned fuel to enter the exhaust system. The unburned fuel ignites inside the converter and could result in a partial or complete meltdown of the ceramic catalyst. Spark plugs and spark plug wires should be checked regularly and replaced if damaged or if wires are worn or cracked.
Oxygen Sensor Not Functioning Properly.
An oxygen sensor failure can lead to incorrect readings of exhaust gasses. The faulty sensor can cause a too rich or too lean condition. Too rich and the catalyst can meltdown. Too lean and the converter is unable to convert the hydrocarbons into safe elements and may not pass a state inspection.
Road Damage or Broken Hangers.
The catalyst inside a catalytic converter is made from a lightweight, thin-walled ceramic. It is protected by a dense insulating mat. This mat holds the catalyst in place and provides moderate protection against damage. However, rock or road debris striking the converter, or improper or broken exhaust system support can cause a Catalyst Fracture. Once the ceramic catalyst is fractured, the broken pieces become loose and rattle around and break up into smaller pieces. Flow is interrupted and backpressure in the exhaust system increases. This leads to heat build-up and loss of power. Possible causes of a catalyst fracture are road debris striking the converter, loose or broken hangers, potholes or off-road driving.


A catalytic converter will rarely fail without a problem or malfunction occurring somewhere in the emission system in front of the converter. It is important to determine what caused the converter to fail so that the problem can be fixed and to prevent a recurrence of the failure.



Converter Meltdown.
This is an example of a converter meltdown. The converter was super-heated due to a raw fuel condition in the exhaust flow. The excess unburned fuel ignited when it struck the hot ceramic catalyst and drove the temperature far above the normal operating condition of the converter. The ceramic catalyst is unable to withstand the extremely high temperature and begins to melt. The ceramic collapses and the converter is destroyed. The melted ceramic may block the exhaust flow and cause additional damage to the engine. A converter glowing red-hot, or evidence of heat discoloration, confirms this situation.

The condition that led to this converter meltdown could be the result of a number of malfunctions including faulty oxygen sensor, an incorrect fuel mixture, worn spark plugs or plug wires, a faulty check valve, incorrect ignition timing, sticking float, faulty fuel injectors or other ignition malfunctions.


Carbon Deposits.
This is an example of a converter with carbon deposits in the ceramic catalyst. This is usually a result of oil or antifreeze entering the exhaust system or a too-rich fuel mixture. The heavy carbon deposit clogs the converter and reduces exhaust flow. This increases backpressure and causes the entire exhaust system to heat up. The heat backs up into the engine compartment and may result in a number of heat-related engine problems.

Mild carbon scoring may do less damage to engine components but it may seriously affect the converter’s ability to reduce harmful emissions. It could easily cause a vehicle to fail an emission test.

Carbon deposits may be the result of faulty valves, worn piston rings, worn or leaking gaskets or lead in the fuel.


Catalyst Fracture.
This is an example of a catalyst fracture. The ceramic became loose, cracked and began to break down. The pieces began to obstruct flow, creating backpressure and increasing the heat in the exhaust system. There is evidence of a partial meltdown in this example due to overheating.

The initial cause for this damage could have been road debris striking the converter based on evidence of impact on the converter shell. In some cases, if the protective mat that holds the catalyst in place is directly exposed to exhaust gasses, it could deteriorate and allow the catalyst to fracture. The Car Sound converter uses two recessed cavities in the body to hold the protective mat out of the exhaust flow to prevent any deterioration. The mat stays in place and the catalyst is held firm.







Catalytic Converter Info




 

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I've experienced 2 melted cats in cars I've owned. Both times it was from a misfire. The mazda6 had a bad coil and a camaro had a bad plug wire.
 

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Thanks for this info. I'm goign to be pulling my precats out this weekend as the rear bank code 421 popped and my car has been throwing misfire codes for cylinders 1 and 3 as well. Sometimes it throws the codes and my engine dogs, sometimes it runs fine. Its weird. Either wya the cats are being gutted and the CEL eliminator is going on.
 

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Thanks for this info. I'm goign to be pulling my precats out this weekend as the rear bank code 421 popped and my car has been throwing misfire codes for cylinders 1 and 3 as well. Sometimes it throws the codes and my engine dogs, sometimes it runs fine. Its weird. Either wya the cats are being gutted and the CEL eliminator is going on.
I am looking into doing this, but have never done anything with cats before. If there's anyway you could snap a few pics when you do it, and offer any tips, I know it would be GREATLY appreciated. Also, please let us know what CEL eliminator you get, and if it works. I really want to gut my cats, but I wouldn't be able to do it on my own without some pics and instructions. Are you pulling the cats off, or just going to gut them while still on the car?
 

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I'm going to pull them off so I know they are completely hollowed. I have a buddy who did the same thing to his TransAm and is going to help me. I'll try to get pics but only have a cell camera.
 

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there was a guy on here a while back, that gutted his precats while still attached to the motor with a screwdriver and a crowbar...i think. i know the hardest was the front precats, he went through the O2 bung for this one. the rear precat collector was removed and jabbed from the bottom. i dont remember if he had pics or not, but im still afraid to this on the front precat because i'd be jabbing in there blindly.
 

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TCS OFF & Stock Y-Pipe

"Any fuel that leaves the combustion chamber unburned will enter the exhaust system and light-off when it reaches the catalytic converter. This can super-heat the converter far above normal operating conditions and cause a meltdown." (as per Chikoo original post). If you drive around without the Traction Control button pushed you may send raw fuel down the exhaust because ignition does not occur when tires spin.. It is better when TCS OFF is displayed on intrument panel.
Also stock exhaust Y pipe is a T pipe causing interference between banks.
See pictures of my Stock 2006 Mazda 6 wagon V6 and new Y-pipe.
 

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You will not get a response from BigAlDJ as he has been banned from this site. I can tell you though that he didnt have specific plans he just wanted that very restricting stock y pipe gone.

Im considering having this done too but when you buy MSDS headers (which im planning on within the next year) you get a y pipe. Therefore spending $600 on a custom y pipe just doesnt make sence to me.
 

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How u going to pass emissions?? I need to replace all my cats and 02 sensors I'm thinking...but headers and a high flow would be nice
 

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^^ Ontario is changing the way testing is done on 1997 and newer cars. They will no longer be using the dyno & sniffer. Instead they will be plugging into the ODB ports and checking for emission codes & to make sure all sensors are workong correctly. So in theory all you need to do is put in a high flow cat or 2 and mount O2 sensors accordingly & passing emissions should be no problem.
 
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