New Catalytic Converter Gives Noise When Accelerating – Why?

It is not every day you find yourself in need of replacing a catalytic converter for your car. When you finally take your car to a mechanic, and they advise on replacing the catalytic converter, you simply agree because they are the experts. But as soon as you pick up the car, you hear some noise coming from the catalytic converter area. Of course, you will assume the new catalytic converter is making this noise.

In our article today, we take a look at the catalytic converter issue of making noise when you accelerate. This is an issue reported by quite a number of car owners and drivers. After picking up their cars from the dealership where a new catalytic converter was installed, they report hearing noise, especially when accelerating.

To understand why a newly installed catalytic converter can make noise when you step on the gas, we will first need to appreciate how this car part works. This will help us know which parts of the converter are likely to make noise and why they do. Getting deeper knowledge on this car part helps you know how to correct this problem.

Understanding Catalytic converter

A catalytic converter is simply an exhaust emission control unit installed in all modern cars to convert harmful engine exhaust gases into less toxic gases. In your car, the catalytic converter is located under, and this may explain why many car owners know little about it.

A catalytic converter can either have a honeycomb or a beaded-shaped piece coated with a metal catalyst. The metal used to coat the converter's inner components is palladium, rhodium, or platinum. The catalytic converter is made effective by the chemical reaction taking place between the metal catalysts and the NOx gases. This reaction separates nitrogen and oxygen from the harmful nitrogen oxides.

The first part of the reaction in the catalytic converter allows the extracted oxygen to be released into the environment while trapping the nitrogen gas. The second reaction phase inside the converter involves reducing the unburnt hydrocarbons and carbon monoxide. This reaction involves burning these harmful carbons over the hot metal catalyst.

The catalytic converter installed in your car is designed to last around 10 years or 100,000 miles. Factors affecting the converter's effectiveness and durability include the miles covered, engine tuning, and, of course, the quality of the part.

When you notice your car to be sluggish and reduced acceleration, it is time to consider replacing the catalytic converter. The other symptoms to look out for include the smell of rotten eggs, extreme heat coming from the car's undercarriage, and dark smoke from the exhaust. While this part is easy to neglect, it plays a crucial role in the overall optimal performance of the vehicle. Replacing it is essential whenever you detect the above symptoms.

Many drivers will drive their vehicles to a dealership to have the catalytic converter replaced. The dealership will check whether the part is still under warranty and proceed to disassemble it. In some cases, the newly replaced catalytic converter can be accompanied by some new problems. As mentioned earlier, you may find the vehicle to make noise when you accelerate.

What causes the new catalytic converter to make noise?

Car owners have reported hearing noise or rattling from the catalytic converter region. Even though the noise would be expected to be heard from an old converter that has gone bad, quite a number of drivers report hearing this noise from newly installed converters.

Ideally, a new catalytic converter should not make any noise or issues. After all, it is new and should be without defects. Let us look at the possible causes of this problem and the reasons behind it.

1) Loose heat shield

The heat shield casing encloses the ceramic honeycomb and the oxidation and reduction catalyst inside a catalytic converter. This heat shield ensures that the enclosed parts work as intended and that the catalytic converter works as a unit. Besides ensuring the converter remains a single compact unit, it also prevents it from making noise. Such noise is bound to be made by the car's vibrations, especially the exhaust system.

The heat shield is riveted and welded into place. If there is a problem with the heat shield, the catalytic converter will make noise, and a lot of it when you accelerate. Remember, the catalytic converter generates a lot of heat.

Solution

The answer to a rattling heat shield of the catalytic converter is simply to fix it. If you neglect this noise coming from this crucial exhaust system part, the surrounding parts, such as the floor mats and carpets, can melt, which can then cause a fire. A loose catalytic converter heat shield should be repaired as soon as possible.

If the heat shield damage is extensive, you should check whether the catalytic converter is under warranty. It is easier to have this part replaced than trying to repair it. In many cases, though, where this problem arises, replacing the bolts should do the trick.

2) Poor airflow

A catalytic converter is a complex unit whose inlet and outlet flow must always be optimal. This means the converter will develop issues if there is some sort of blockage. For a new catalytic converter that is making noise when you accelerate, the problem could be lying with the airflow inside the unit.

The problem is usually caused when the engine is supplied with low-octane gas. The lower the octane level in your fuel, the harder it is for the catalytic converter to perform optimally. High-octane level gas is ideal for your car's engine.

Solution

The answer to this issue is to simply switch from lowest-octane gas to high-octane gas. Running high-octane fuel through the vehicle's fuel system helps clear the airflow, and the noise will fade away. Some mechanics advise using additives to help clear the airflow in the cat.

3) Damaged honeycomb structure

The honeycomb structure inside the catalytic converter is complex and brittle. When subjected to years of use, it will likely break down, which usually causes it to rattle, thus making noise when you accelerate. The honeycomb structure can be damaged when there is a direct impact on the catalytic converter.

As observed earlier in this article, the catalytic converter is on the underside of your car. If you drive on rough terrain with boulders, the undercarriage is likely to be hit or scratched. The cat is likely to be a recipient of these hits, and this can cause damage to the honeycomb structure. This kind of damage will have the same effect as when the honeycomb breaks down because of age. The catalytic converter will make noise when you step on the gas pedal.

Solution

The answer to this problem is to simply replace the catalytic converter. You should take your car to a mechanic and have the cat replaced as soon as possible. The temporary answer to the problem is to use a hammer and probe the catalytic converter to establish where the rattle originates. You should then use a screw on the spot to try and hold the honeycomb in place. This screw should hold for some time as you prepare to buy a new cat which can be pricey.

Even though the cat is new or the vehicle is new, damage to the honeycomb structure causes this exhaust part to malfunction. Your car's exhaust emissions will be harmful, and you will be violating EPA and other related emissions tests, regulations, and laws.

4) A faulty catalytic converter

As unlikely as it might be, you may fall victim to an unscrupulous mechanic or dealership. As you may know, catalytic converters are quite a prize for car part thieves. When you take your car to the mechanic, you will likely be at a waiting bay while they work on your car. For a rogue mechanic, this can be the perfect setup to install on your car a faulty cat.

Solution

It doesn't always mean you have been scammed whenever you hear a new catalytic converter making noise when you accelerate. It can be that the cat has a genuine structural defect, and it needs to be replaced. The best way to avoid and resolve this problem is to take your car only to an authorized dealership. A defect on the cat can be a sufficient reason for a replacement, as all genuine catalytic converter manufacturers have backed their products with a warranty.

Conclusion

A new catalytic converter is unlikely to be blocked as to require any sort of cleaning. You should not rush to use sodium hydroxide and additives to clean the cat. Unlike some other car parts, installing the catalytic converter is unlikely to be done wrong as to cause it to make noise.

Check for the most likely causes of the noise, as highlighted above. Before you conclude it is the catalytic converter making the noise, have a professional mechanic test your car. This will ensure that you don't misdiagnose the problem.