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Engine misfires are more often than not caused by spark plugs and other ignition parts, but sometimes, an engine misfire can be caused by a bad or clogged catalytic converter.

It can be difficult to determine the issue behind a misfire because clogged catalytic converters are not the most common reason. This article will provide you with all the relevant on catalytic converter misfire, and the symptoms of a bad catalytic converter cause misfire to look out for!

What Is a Catalytic Converter?

The purpose of a catalytic converter is to convert harmful compounds found in your vehicle’s emissions into safe compounds, like steam.

It’s able to do this by splitting up the unsafe molecules so that they are released into the air in a safer manner. In order to do this job, your catalytic converter includes reduction catalysts and oxidation catalysts.

The reduction catalysts remove oxygen to reduce nitrogen oxides, while the oxidation catalysts add oxygen to remove carbon monoxide.

Both nitrogen oxides and carbon monoxide are dangerous on their own, but the molecules can be broken up to create safer emissions.

Although all catalytic converters serve the same function, there are two main types of converters your vehicle might have: a two-way or three-way.

Most modern-day engines will use the three-way catalytic converter because it also includes the reduction catalyst. Diesel engines, however, use two-way converters.

Can a Clogged Catalytic Converter Cause a Misfire?

Yes, a clogged catalytic converter can cause a misfire. However, it is not the sole reason for a misfire occurring, and nor is a misfire the only symptom of a bad catalytic converter. So, why does a clogged catalytic converter cause a misfire?

Whenever a catalytic converter gets clogged, the engine will create toxic byproducts such as hydrocarbons, carbon monoxide, and nitrogen oxides. These harmful toxins that are released are not what causes the misfire however, it’s basically because there is limited power and smoke is unable to leave the car as it should.

The clogged catalytic converter forces the car to lose its power, which makes it far more difficult for smoke to exit through the car’s exhaust pipe and engine.  


How Does a Catalytic Converter Get Clogged?

More often than not, a catalytic converter will become clogged whenever oil or antifreeze is able to enter the vehicle’s exhaust system.

With this excess oil and antifreeze, a thick layer of carbon and soot coats and clogs the passage in and out of the catalytic converter. Therefore, the result is two separate problems.

The first problem is the carbon and soot deposits preventing the catalytic converter from removing harmful emissions. And the second is the backpressure increases because of the exhaust flow being restricted. 

This then further increased pressure will cause the heat and exhaust fumes to go back inside the engine, potentially creating internal damage.

Other Reasons for an Engine Misfire

As we’ve already touched on, a clogged catalytic converter is not the most common reason for engine misfires. Before checking out the converter, it’s better to look at the following vehicle parts which are most commonly associated with an engine misfire issue:

  • Spark plugs
  • Carbon tracking
  • Other ignition-related problems

Spark Plugs

Spark plugs are the most common cause of engine misfires. The spark plugs role is to deliver electric current from the ignition to the combustion chamber, which therefore allows the ignition of the fuel and air mixture.

If spark plugs have worn down, been installed incorrectly, or mishandled in any way, a misfire can easily ccur.

The mishandling of spark plugs can cause them to leak air, resulting in an altered ratio between air to fuel. Hence, leading to an engine misfire.

Carbon Tracking

Carbon tracking, also referred to as flashover, is another very common reason an engine will misfire. Carbon tracking occurs whenever oil, erosion, dirt, or moisture, ground the spark at the ignition point of the spark plug insulator.

Most modern-day spark plugs are designed to be able to avoid this issue, but older vehicles may still have to face the issue.

Other Ignition Problems

Sure, spark plugs are considered the most likely component to blame for any form of ignition problems and engine misfires, but there are a few more potential ignition system problems causing the misfire.

These ignition system problems that can result in eninge misfire could involve coil packs, crankshaft position sensors, and wiring.


How to Determine if a Clogged Catalytic Converter Is Causing a Misfire?

Because there are so many possibilities as to why engine is misfiring, it can often be difficult to determine the exact cause. We recommend looking at the other reasons for an engine misfire just described to rule out the more common causes first.

After checking those, you can switch your focus to the catalytic converter and looking for signs that it is indeed at fault.

Look for Other Signs of a Bad Catalytic Converter

It’s important to pay attention to any of the other signs of a bad catalytic converter. You don’t necessarily have to notice all of the symptoms, but if you notice a couple then it is a great indication that you have a clogged catalytic converter causing misfire.

Here are the other signs you can look out for:

  • Reduced power when accelerating
  • Increased emissions
  • Poor engine performance
  • Rotten smells
  • Check engine light on

Reduced Power When Accelerating

Whenever your clogged catalytic converter causing misfire, you will likely experience a loss of power whenever you are driving uphill or accelerating.

You might have already taken your vehicle to a professional mechanic due to reduced accelerating power, but it can be difficult to diagnose the cause as the bad catalytic converter because the part is partially obstructed.

There’s a way you can perform run a test at home to try to determine if the clogged catalytic converter is the cause for this reduction in acceleration power.

To do so, ask your partner or neighbour politely to get your vehicle’s RPM between 1800 and 2000. Then place your hand at the end of the exhaust to see if it is hot. If it is, you likely have a clogged catalytic converter.

If it does not feel hot, it either is not clogged enough yet or it is not clogged at all. Keep in mind that this test does not replace the value of having your vehicle inspected by a professional, but it can help narrow out some potential causes at home.

Increased Emissions

Increased emissions are also one of the most common indications of a clogged catalytic converter. When catalytic converters are faulty, they will be unable to break apart molecules properly, which leads to gases being admitted into the exhaust system.

As soon as you notice additional carbon emissions exiting your vehicle, you are likely to have a clogged catalytic converter cause misfire.

Poor Engine Performance

As already touched on, clogged catalytic converters result in an increase in back pressure, which in itself reduces the performance of the engine. Poor engine performance results in symptoms like shaking when driving, sudden pressure outbursts, or even occasional stalling.

Rotten Egg Smell

If your catalytic converter has been clogged for a while, you will probably start smelling an odour which can be quite similar to the smell of rotten eggs. This sulfuric smell typically comes from poorly converted exhaust gases.

Check Engine Light Is On

Of course, the check engine light flashing can come on for a whole variety of reasons. However, if you cannot pinpoint why the check engine light is on, it could be the catalytic converter that is the issue.

You should take your vehicle to see a professional mechanic to help determine if the check engine light is on due to a clogged catalytic converter.

Take Your Vehicle to See a Professional Mechanic

If you suspect that your catalytic converter is clogged after performing the above checks, it’s time to take your vehicle to a professional mechanic. Only from a mechanical professional will you be able to confirm that a clogged catalytic converter is the reason your engine is misfiring.

FAQs (Frequently Asked Questions)

Will a bad catalytic converter throw a misfire code?

Yes, a bad catalytic converter is a likely cause of an engine to misfire. A blocked catalytic converter will typically overheat, which can cause damage to your car’s engine and result in a misfire.

Can bad cats cause random misfire?

An engine misfire is a surefire symptom of a bad catalytic converter. Whenever your car has a random misfire, it indicates incomplete combustion within the engine’s cylinder, and this could be due to the catalytic converter not functioning effectively.

What are the symptoms of a bad catalytic converter?

There are multiple signs of a bad catalytic converter, and these include reduced power when accelerating, increased emissions, poor engine performance, rotten smells, and the check engine light coming on. Although the latter is hard to pinpoint, if you check other parts of the car, it may be the catalytic converter.

What problems can a bad catalytic converter cause?

A compromised catalytic converter can cause many problems which include sluggish engine performance, reduced acceleration, dark smelly exhaust smoke (like rotten eggs), and Excessive heat under the vehicle.