Bad Catalytic Converter: Common Causes and How To Fix It

A bad catalytic converter can cause reduced acceleration and hurt the performance of the engine. Worse still, a damaged converter may allow the release of harmful gasses into the environment, which may cause havoc to plants and animals.

Bad Catalytic Converter

This is why you need to know the reasons why a catalytic converter will fail and, most importantly, how to fix it. In this article, we’ll not only discuss the causes and fixes of a damaged cat but answer important questions about it as well.

What Are the Causes of a Bad Catalytic Converter?

The causes of a bad catalytic converter are unburned fuel making its way into the exhaust system, water in the fuel, bad roads, extreme heat, and a malfunctioning oxygen sensor. Other causes include old age and foreign objects in the exhaust system.

– When Sparks Plugs Lose their Timing and Misfire

Spark plugs ignite the essential air and fuel mixture in an engine to produce as part of the combustion process to power the vehicle. However, when the spark plugs lose their timing, the fuel may escape the combustion chamber into the exhaust system.

There, the unburned fuel could ignite and burn due to the extremely high temperature in the cat converter. The burning fuel may then produce excessive heat, which would melt the ceramic cat converter.

– When Water Gets Into the Fuel

Another element that can damage a cat converter is water. One of the most popular ways water finds its way into fuel is through condensation. This happens when the temperature outside the fuel tank is different from the one inside, which causes droplets of water to form between the fuel and the tank’s headspace. These droplets then get into the fuel and escape the combustion process, eventually making their way into the cat converter.

Once inside, the water causes the converter to rust as it reacts with the air. Another way water gets into your fuel tank is at the fuel pump when you have a leaking gasket. The gasket is designed to keep air and other debris out of the fuel tank to avoid contamination. Thus, if it is broken, it may allow air into the fuel tank, which can end up in the cat converter.

As we’ve already discovered, water in the cat converter is bad news as it can cause it to rust. Sometimes, this may not be easily detected until a failed emissions test or the converter is completely damaged.

– Bumpy Roads Can Destroy the Honeycomb of the Converter

When the exhaust is hanging too low or the potholes are too big and deep, the honeycomb of the converter could hit the road and suffer damage. This same problem can be caused by an overly high-speed bump that scrapes the honeycomb under the car.


The honeycomb inside the converter is a lightweight ceramic material with thin walls which can easily break. It is held in place by a dense insulation mat which protects the device from external damage.

However, the security this mat provides can be compromised and the fragile honeycomb broken into pieces. These pieces move inside the converter as the vehicle is in motion and interrupt the flow of exhaust gases backpressure. This then leads to the buildup of excess heat and subsequent loss of power.

– A Malfunctioning Oxygen Sensor Sending False Signals

A bad oxygen sensor means that the vehicle’s ECU (the brain of the car) will receive false readings of exhaust gases. This could lead to an improper air-fuel mixture inside the engine; the mixture may be too rich or too lean.

Causes of Bad Catalytic Converter

When the air-fuel mixture is too rich, it allows fuel into the exhaust system, which can burn the catalytic converter as we encountered in the earlier paragraphs. However, when the air-fuel mixture is too lean, the converter won’t be able to convert hydrocarbons to safe emissions.

An oxygen sensor helps the engine to get the right amount of air and fuel mixture to cause proper combustion. However, when it is faulty, it doesn’t only damage the converter but also results in rough driving and idling as well.

– Foreign Objects Making Their Way Into the Exhaust System

When foreign objects such as dirt and small stones get into the exhaust system, they can end up damaging some vulnerable parts of the cat converter. One such part is the fragile honeycomb, which plays an essential and highly pivotal role in the conversion of the poisonous gasses.

These foreign objects can access the converter through holes and cracks in the exhaust system. Sometimes a faulty exhaust filter is to blame as it allows fine grains of dust or sand to seep through and damage the converter.

– Oil and Antifreeze Can Damage the Converter

If oil or antifreeze seeps into the exhaust system, it produces a thick soot that covers the honeycomb of the converter blocking the air passages. This hampers the work of the catalytic converter as it is unable to convert the poisonous gasses into less harmful ones.

Antifreeze Damages Catalytic Converter

Also, the blockage of the air passages leads to an increase in backpressure, which is the resistance to the flow of exhaust gases. Excess backpressure can damage the engine as the exhaust gases get sucked back into the engine.

This affects the next combustion process and leads to loss of engine power and overheating in the engine. Aside from a bad cat converter, damaged gaskets, broken seal valves, and other failed components of the engine can cause a malfunctioning catalytic converter.

– Old Engines or Engines That Work Outside Their Parameters

When engines get too old or overwork for a long time, they begin to malfunction and thus produce by-products that can damage the converter. Stuck rings, worn filters, and broken valves can allow could either allow harmful substances to pass through or produce the substances themselves.

The worn-out components of the engine may also cause engine misfires, incorrect air/fuel mixture, or bad timing, which may be detrimental to the catalytic converter.

– Catalytic Converters That Are Past Their Prime

Old catalytic converters can fail, which is a normal phenomenon for all car components. Cat converters can last for up to 100,000 miles or 10 years; however, it could even be shorter.

Factors such as engine tuning, mileage, and even bad roads can affect the lifespan and integrity of the device. Thus, it’ll begin to malfunction and eventually damage the engine if you don’t act quickly to salvage the situation.

What Are the Methods To Fix a Bad Catalytic Converter?

The methods to fix a bad catalytic converter include using fuel additives, driving your car hard until the engine reaches a high temperature, and cleaning the converter. However, note that these methods are just for minor problems. Major problems will require a catalytic converter replacement.

– Adding Additives to Your Fuel To Clean the Converter

You can pour fuel additives such as Cataclean into your fuel to clean the device. This method also requires that you drive the car around for about 15 minutes to ensure the cleaner does a thorough job. Another additive that’ll do quite a good job is a lacquer thinner. However, with this product, you’ll have to drive for about 150 miles for it to take full effect.

– Driving Your Car Hard Until the Converter Becomes Hot

This method is for slow drivers and people who usually take short trips. Actually, frequent short trips can also cause the converter to fail because it doesn’t get hot enough to function properly.

Fixes of Bad Catalytic Converter

Thus, the best way to solve the problem is to drive the car at a faster pace (but obeying all speed limits) and for a longer distance. This could bring the device to its optimal temperature and enable it to burn away the hydrocarbons in the exhaust flow.

– Cleaning the Converter of All Dirt and Debris

Another way to fix a clogged catalytic converter is to remove it and clean it. Removing a cat converter is not that difficult; all you have to do is remove a few screws and the device will come off. Once it is off, use a pressure washer to clear all the debris inside the clogged catalytic converter and wipe off the water.

Frequently Asked Questions

– What Are the Telltale Signs of a Bad Catalytic Converter in Ford?

The telltale signs of a bad catalytic converter in Ford vehicles include a rotten egg smell, dark exhaust smoke, poor acceleration, and reduced engine performance. Also, the check engine light is likely to illuminate and the engine may suffer a breakdown in the worst scenario.

– Can a Bad Catalytic Converter Unclog Itself Back to Factory Settings?

Yes, a bad catalytic converter can unclog itself back to factory settings when you pour Catacleaner into the fuel and allow it to run through the entire exhaust system. However, do this only when the device begins to show overheated catalytic converter symptoms like bad acceleration and fuel efficiency.

Bad Catalytic Converter Solved

What Are the Common Causes of Bad Catalytic Converters and How Can They Be Fixed?

One of the common causes and fixes for bad valve bodies in vehicles is dirt and debris accumulation. Over time, these particles can clog the valve body, affecting its function. Another cause can be wear and tear, leading to internal damage. Fixing such issues may involve cleaning the valve body or replacing it altogether. Regular maintenance and ensuring the use of clean fluids can help prevent these problems.


So far, we’ve learned what happens when a catalytic converter goes bad and how to fix it. Here are the major highlights of what the article has discussed:

  • A bad cat converter could be caused by faulty spark plugs, water in the fuel, foreign objects in the exhaust system, and bumpy roads.
  • Other causes include oil or antifreeze entering the exhaust system, old cat converters, and older car engines that are past their prime.
  • To fix the problem, you can either add additives like a cat cleaner or lacquer thinner to the fuel to unclog the converter.
  • You can also remove the device and clean it, after which you can put it back in its place.
  • Symptoms of a bad or faulty catalytic converter in Ford vehicles include the check engine light turning on, poor fuel economy, and rattling noises in the engine.

Driving your vehicle hard and for longer distances can also help eliminate some of the symptoms associated with a failed converter.

5/5 - (15 votes)
Ran When Parked