Skip the auto shop - Our mechanics make house calls

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 1000 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
  • Home
  • Questions
  • 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: Throttle suddenly goes out

Hi there, thank you for asking about your 2003 Mercedes-Benz S55 AMG. This is usually caused by a failing throttle body. The throttle motor or sensor fails and will cause this to occur. If the motor cannot move the throttle...

Q: When looking at the Truck Engine my fan spins to the left which way would I turn the bolt to loosen it on a fan clutch

Always loosen the fan in the same direction it turns. You may need to have the holder and large wrench. You may need to shock the fan to the left while holding the fan pulley. I usually leave the belt...

Q: Loss of power won't go over 35 mph - 1999 Dodge Ram 1500

This may be a sign of low fuel pressure, a failing mass air flow sensor or potentially a clogged catalytic converter. As you may already know, the catalytic converter converts toxic exhaust gases into less harmful pollutants that are suitable...

Related articles

What Causes Hoses to Leak?
While the largest part of your engine is mechanical, hydraulics plays a significant role. You’ll find fluids at work in a number of different areas. Your car's fluids include: Engine oil Transmission...
P2428 OBD-II Trouble Code: Exhaust Gas Temperature Too High Bank 1
P2428 code definition A P2428 trouble code signifies that the PCM has detected a problem in the exhaust gas temperature sensor circuit in bank 1, which subsequently contains the number one...
P2103 OBD-II Trouble Code: Throttle Actuator Control Motor Circuit High
P2103 means there is a fault with the throttle actuator control motor circuit, likely due to a defective electrical component or part.