To unclog a catalytic converter, get onto a highway, and drive at high speed for a couple of miles, coming to a stop and starting again several times. Repeat two or three times, giving the converter a chance to expel debris.
- Drive the car at highway speed
Take your car onto a highway, and drive it at the speed limit for 1 to 2 miles. Check your mirrors to make sure that a sudden deceleration is safe, and slow the car down quickly. Move over to the shoulder to complete this if necessary. Accelerate back to highway speed, repeating the process several times during the 2 miles. Estimate whether acceleration has improved; this is the best sign that you see while driving that the clog is gone.
- Try a higher speed
Resume driving on the highway if the clog is still present. Check your mirrors and the surrounding lanes to make sure that driving somewhat above the speed limit is safe, and then drive up to a mile at that speed. Check your mirrors again, then slow to about half your speed and then accelerate again, going another mile.
- Monitor your fuel economy
Measure your mileage the next two or three times you fill up your car with gasoline. Consider the performance of your car during acceleration, and use these two factors to determine whether replacing the catalytic converter is necessary.