If your catalytic converter rattles, it’s a symptom that it may be worn out or damaged internally from excess rich fuel mixtures.
Additionally, the catalytic converter can fail when the honeycomb meshes on the inside break or collapse apart.
According to statistics, in the U.S., over 2800 were killed and approximately 400,000 injured as a result of distracted driving. (Source)
In this article, I shall be discussing the common symptoms of a failing converter and different ways to fix the problem.
What is a Catalytic Converter?
A catalytic converter is a device that helps control the pollutants and toxic gases contained in exhaust gas into less harmful pollutants.
The harmful compounds in this case are:
- Carbon monoxide
- Nitrogen Oxides
The carbon monoxide is converted into carbon dioxide through a redox reaction, while nitrogen oxide is converted into nitrogen and oxygen; lastly, the hydrocarbons are converted into water and carbon dioxide. (Source)
Essentially, when these toxic compounds from the engine reach the catalytic converter, they’re forced through an inner honeycomb lined with catalysts that spark a series of chemical reactions.
This converts the toxic compounds to fewer toxic compounds.
What Kind of Noise Does a Bad Catalytic Converter Can Make?
If you hear rattling sounds coming from underneath your car, it could be possible that the catalytic converter is damaged.
Honeycomb mesh could be broken or collapsed.
When you switch on the ignition, these pieces of broken honeycomb mesh will vibrate, resulting in rattling noises.
The damage could be as a result of age or simply from excessively rich fuel mixtures.
And lastly the rattling noise will become worse over time.
What are the Signs of a Failing Catalytic Converter?
The are several tell-tale signs of a failing catalytic converter that you should watch out for. They include:
- Check Engine Light: If your check engine light is on and you are sure that it’s not a problem to do with the oxygen sensor, emission-related code, or engine misfire, then have your mechanic check your cat converter.
- Misfiring: a faulty or missing cat will cause gasoline in the engine to heat up to the point that it actually ignites. Misfiring can damage the engine, and you should make sure that your mechanic checks the engine.
- Rattling noises from underneath the vehicle: a rattling sound from beneath your vehicle is never a good sign. When a cat converter is damaged, it can cause the mesh honeycomb to collapse or break. After turning on your vehicle, these pieces will vibrate and rattle.
- Decrease gas mileage: if the gas mileage has significantly dropped, it could a sign of a clogged catalytic converter or other mechanical problems on your car. A clogged catalytic results to reduced airflow that causes the engine to burn extra fuel. This not only makes it a pain at the pump but also makes the clog worse.
- Dark smoke and rotten egg smell: a clogged converter makes it hard for exhaust to exit your car, resulting in a thicker and darker build-up. Because fuel contains sulfates characterized by rotten egg smell, a clogged catalytic converter causes buildup that makes the undetectable odor detectable.
- Failed Emission Test: several states here in the USA have laws requiring a diagnostic check to pass the emissions test. If the cat is faulty, the test will fail.
What Are the 3 Most Leading Failures of a Catalytic Converter?
Well, converters never fail on their own, and failure indicates a symptom of a larger problem.
That’s why it’s always important to figure out the main cause of the failure and perform the repair before installing a new converter.
Catalytic converter failures can be categorized into three:
- Structural damage
- Overheated or broken converters
- Oil-fouled/coated substrate
The main cause of the structural damage to the cat is road debris.
Visual inspection on the converter shield will indicate some structural impact. Other possible causes include
- Thermal shock
- Missing O2 sensors
- Stress fractures
Any malfunction resulting from unusual high 02 and CO or HC levels entering the converter will significantly spike the temperatures.
Some possible culprits for high HC include:
- Low compression
- AFR cylinder imbalance
- Poor spark or no spark
The oil-fouled substrate, also known as catalyst poisoning main occurs when the converter is exposed to emission containing compounds that coat the surfaces until it no longer functions well.
There are several causes of oil-fouled substrate build-up, and they include:
- Internal coolant leaks
- Improper additives or fuels
- Excess carbon buildup in the exhaust
- Excessive oil consumption
How to Quiet a Rattling Catalytic Converter
Whether it’s clogged or faulty, there are several ways you can make the catalytic converter quieter. Below are methods to help you reactivate the old one and make it perform like new.
How to Stop the Rattles
When your catalytic converter is going to fail, it will cause rattling noises.
If you regularly inspect it, the chances are that it won’t fall apart, and you’ll be in a position to repair it before it’s too late.
However, you will need a mechanics stethoscope to identify the loose pieces inside the system.
To fix the loose parts, drill a hole at each location that’s affected and insert a drywall screw in it. This screw will hold the loose parts in place, stopping the rattling and extending the converter’s lifespan.
Regularly Clean It
You should check regularly the catalytic converter for carbon build-up and mild oil fouling and clean it.
Something like Cataclean 120007 Complete Engine will cost you less than $30.
Simply mix it with the gasoline, and it will remove those toxic deposits from the engine and converter as well.
However, if the cleaner doesn’t solve the problem, it’s most likely to be clogged with sulfur and phosphorous from the fuel and oil.
According to research soaking the converter in dilute citric acid will remove harmful deposits with affecting platinum inside the converter. (Source)
Use Lacquer Thinner
Lacquer thinner is a highly effective tool for cleaning clogged catalytic converter before it loses efficiency.
Simply add one gallon of the cat cleaner to the gas tank and then top up 10 gallons of gasoline.
Likewise, you should then drive the car for approximately 150miles and keep the RPM at 2500 or higher for about 30 minutes.
After the lacquer has worked its magic, you should expect improved performance, and if possible, the rattling shouldn’t be anymore.
Below is a YouTube video on how to use the cat cleaner.
Fuel additives are can also be great lifesavers- check out my guide on the best additives to the quiet engine and catalytic converters.
Get a New Catalytic Converter
Additionally, if everything else fails, you will have to dig deeper into your pockets and get a new cat.
You can install the converter yourself, but here is what you should do- purchase a direct fit converter and not a universal fit.
This is because universal fit requires welding while a direct fit only requires bolts. Below is another video on how to DIY installation.
Final thoughts on Catalytic Converter Rattles
Above are the best methods on how to deal with catalytic converter rattles to achieve quieter rides.
Lastly, fixing the cat helps reduce air pollution and sound pollution, achieving quiet rides and reducing possible distractions on the highway.
Meet Mike O’Connor, (a DIY enthusiast), living in Cincinnati, a city ranked as the noisiest in the USA.
As a work from home dad, I have a first hand experience of how noise can truly affect your well being.
Soundproofing isn’t something that should be taken as a hobby, it should be a skill that every homeowner should be equipped with.
Most of the work documented on this blog comes from purely first hand experience, and the products recommended work as indicated.