EliteCM.net

This DIY will show you how to make an O2 Sensor Defouler for less than $6 bucks. This defouler will get rid of the P0420 code for a bad Catalytic Converter, for those of you who have a test pipe or those of you that like me, gutted their catalytic converter. The defouler will move the secondary O2 Sensor away from the direct flow of gasses in the catalytic converter which will trick the computer into thinking that there is still restrictions in the cat therefore keeping the Check Engine Light from coming on.

One:

Go to Advance Auto Parts and buy one of these spark plug non-foulers. Part # 42009 The package brings two and you will need both.
(http://i1306.photobucket.com/albums/s576/olecram93/IMAG0371_zpsd233979d.jpg) (http://s1306.photobucket.com/user/olecram93/media/IMAG0371_zpsd233979d.jpg.html)

Two:
Place one of the non-fouler in a vise. If you don't have a vise ask a buddy to hold it in place with a pair of pliers.

(http://i1306.photobucket.com/albums/s576/olecram93/IMAG0372_zpsdda1623b.jpg) (http://s1306.photobucket.com/user/olecram93/media/IMAG0372_zpsdda1623b.jpg.html)

Three:

Next, You will need to expand the hole in one of them to 1/2 inch in diameter so that the O2 sensor can fit inside and screw in. The other one will be left alone.

Be careful to not mess up the threads on the sides of the non-fouler. Keep the drill bit as straight as possible.

(http://i1306.photobucket.com/albums/s576/olecram93/IMAG0374_zps95dfdeba.jpg) (http://s1306.photobucket.com/user/olecram93/media/IMAG0374_zps95dfdeba.jpg.html)

(http://i1306.photobucket.com/albums/s576/olecram93/IMAG0375_zpse2152907.jpg) (http://s1306.photobucket.com/user/olecram93/media/IMAG0375_zpse2152907.jpg.html)

Left one was drilled. Right one wasn't.
(http://i1306.photobucket.com/albums/s576/olecram93/IMAG0378_zps65ba58be.jpg) (http://s1306.photobucket.com/user/olecram93/media/IMAG0378_zps65ba58be.jpg.html)


Fourth:

Screw them together. Keep the one you drilled out on top and the one you didn't do anything to on the bottom. They come with two crush washers, i used them but they are not 100% necessary.


(http://i1306.photobucket.com/albums/s576/olecram93/IMAG0380_2_zpsff372ce1.jpg) (http://s1306.photobucket.com/user/olecram93/media/IMAG0380_2_zpsff372ce1.jpg.html)

Fifth:

Take it back to your car, use some anti-seize on the threads, screw the new defouler on your Cat or test pipe and tighten it, then screw the O2 sensor on the end of the defouler and you are done!

Enjoy!

Good write-ups Marcelo.

Thank you sir

this works very well!

I had done this back in the day with my high flow cat on an old exhaust set up. Definitely a good low $$ alternative if you don't have the ability to disable your O2 sensor.