Q: Is the catalytic converter clogged if it starts and runs but rattles kind of when it starts and doesn't accelerate very well?

asked by on

If it starts and kind of rattles when it idles and doesn't accelerate very well as the catalytic converter clogged

My car has 152549 miles.
My car has an automatic transmission.

This is a common description of a clogged catalytic converter. If it is the catalytic converter that is rattling, that means the honeycomb lattice inside the cat has come loose. However, this doesn’t mean the cat is clogged, but it could be. Checking for a clogged exhaust system is fairly simple. Simply put your hand in front of the exhaust outlet and see if there is plenty of air exiting it. If you are not sure it is enough, do this with a good running car that does not have a modified exhaust. It should be as strong as a typical fan in your home. Following this, have someone rev the motor up and see if the air flow out the exhaust increases significantly. If the motor does not rev easily, floor the pedal and see if the RPM’s will rise or stop and not go any further. Revving a motor in this fashion should quickly rev to red line with little effort. If it sluggishly revs, this is another sign you have a clogged exhaust.

If the motor won’t rev, the next thing to do is create an exhaust leak as close to the motor as you can, then rev the motor. It will be very loud, but if it is now able to rev, you have confirmed the exhaust is clogged.

After doing these simple tests, we can get a good idea if the exhaust is plugged. While the catalytic converter is the most likely culprit, other things can occur to clog an exhaust system. The rattle could be another part of the exhaust such as a metal heat shield or broken exhaust hanger.

A lack of acceleration can be caused by a large variety of reasons other than a plugged exhaust. Follow the steps I laid out about and you should be able to come to a conclusion.

To avoid any unnecessary repairs, I recommend having the loss of power inspected by one of our mobile technicians at your own location. Be sure to notify the technician about suspecting the exhaust is plugged.

Good luck!

Was this answer helpful?

Need advice from certified mechanic? Get help now!

Over 1,000 mechanics are ready to answer your question.
The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

Ask a Mechanic
(100% Free)

Have a car question? Get free advice from our top-rated mechanics.

Ask A Mechanic
Over 10,000 questions answered!
  1. Home
  2. Questions
  3. Is the catalytic converter clogged if it starts and runs but rattles kind of when it starts and doesn't accelerate very well?

Get an instant quote for your car

Our certified mechanics come to you ・Backed by 12-month, 12,000-mile guarantee・Fair and transparent pricing

Get a quote

What others are asking

Q: Rough idle, stalls when accelerating, engine shuts down while driving with no fault codes.

Hi there. The issue is the coolant thermostat temperature sensor. The sensor is malfunctioning causing the computer (ECM) to think that the engine is either too cold or too hot and causing the fuel mixture to be off. I recommend...

Q: No acceleration when I press the gas

Hi there. Typically when you have acceleration problem as you are describing it can range from fuel, ignition or transmission problems. If the fuel system is clogged with excessive debris or carbon deposits, it will create acceleration problems, as will...

Q: Car starting then has a power loss.

Hi there. Check all the fluids on your vehicle. Depending on what kind of service was performed on your vehicle will depend on what happened to your vehicle. If you had the engine oil changed, then make sure that the...

Related articles

How Long Does a Heater Control Valve Last?
Keeping the right amount of coolant in a car is essential in keeping the engine at the right temperature. Failing to have the right amount of coolant or even bad elements...
Rules of the Road For Iowa Drivers
Driving on the roads requires knowledge of the rules, many of which are based on common sense and courtesy. However, even though you know the rules in...
How Much Does a Mechanic Make in Vermont?
Automotive technician jobs in Vermont have an average mechanic salary of $37k, with some mechanics earning a salary of $53k.