Dorman 42002 Spark Plug Non-Foulers - 18mm Tapered Seat for Select Models, 2 Pack

These can solve the dreaded P0420 OBDII code (catalyst efficency) by moving the rear O2 sensor out of the direct exhaust stream, so the readings at the sensor are more consistent and normal. Cats are expensive and this will buy time and save money with the side benefit of not having to look at a dumb CEL day and night.

1998 Jeep Wrangler tj, I’ve shortened the exhaust and running a super 40 muffler. I am hitting my cat and was told to buy this. It says it’s a 2 pack but only one fit didn’t matter since I only had one rear o2 sensor after the cat. Install took maybe 5 from start to finish and getting tools. Seems to be made of good quality and for the price you can’t go wrong. I will update after I gut the cat and see if I have a cel light

I used this to move back the oxygen sensor on a truck (off road) with modified exhaust that kept displaying the check engine light because of the converter being opened up. Simple 10 minute installation - No more check engine light.

I'm putting an aftermarket exhaust on my 03' sentra SE-R SpecV because the OEM exhaust manifold has a pre-cat on it and that's not a good thing because its too close to the engine and with age, the pre-catalytic converter will break down and can get sucked into the engine.. So I replaced the manifold and I needed to get these to trick the ECU to thinking everything was alright since one of my 2 catalytic converters is coming off due to it being unnecessary. These fit the new exhaust manifold perfectly but I did have to use a 1/2" titanium drill bit to bore out a bigger hole in one of them for my 02 sensor to fit. After that though I just screwed the modified one into the other one and it fit right in and my 02 sensor is none the wiser while I still have my other catalytic converter allowing me to pass emissions. Definitely recommend this to others needing to do the same thing.

O.K. I did not use these as designed, but rather drilled out the centers large enough for my Miata's O2 sensors to fit into. My check engine light went out and I passed inspection. I later replaced the faulty O2 sensors but these did the trick till I saved up for them.

Installed in o2 bung. Ran car. Engine check light still on. Disconnected battery for half a day. Hooked battery back up. Ran. Engine check light still on. Mad. Cussed. Forgot about it for a few day. Engine check light now off. Happy. Positive review.

Bought these for a friend's Briggs&Stratton lawn mower that was burning so much oil, the plugs stopped working. I was skeptical that this would even light the fuel/air mixture, but sure enough! This won't stop oil burning, just prevent the plugs from getting bad (nearly as quick as they would normally).

I keep getting catalyst codes on my 2007 Jeep Wrangler. Installed the spacers downstream from the catalytic converter and the codes went away. Now at least I know when I get a check engine light that I should actually pay attention!

Somehow i installed one at the downstream for a camry 2003 2.4 se with check engine on all the time even tought i erased it,it will always comes back.. but with the installation before you have to drill a bit with 1/2 bit everything working well... and no lies i am saving on gas. Result maybe won’t be the same for others but for me it worked

They can also be used as an O2 sensor quick and dirty fix. Threading two of them together after drilling them out, you can install them on the end of the O2 sensor to pull it out of the exhaust stream a little bit and make your Subaru stop throwing annoying P0420 codes.

I used these non-foulers for my Honda S2000 in between my O2 sensor and test pipe with a little modifications in order to prevent the engine light. It works great, I've had these for about 6000kms and still no check engine light. I would recommend this product

Took care of my cat code, had to drill it out to fit the O2 Sensor on my 2003 matrix but it works well.

I can't use them because there is no enough space between upstream sensor and car chassis metal,