I saw a few posts about installing spark plug non-foulers on your 2nd o2 sensor before and even a small tutorial of how to do it, which I followed and successfully finished... and I've had no Cat Converter Inefficiency code in the last 3,000 miles since I installed it..
I decided that while I did it myself.. I would take photos in order to create a more in-depth tutorial on how to save yourself $150+ on a new cat... or to help pass a safety inspection
- Drill (Multi or high speed)
- 1/2-inch Titanium Drill bit or bit used for drilling steel
- 18mm Spark Plug Non-Foulers Part No. 42009 (they come in a pair from AutoZone for about $3.99 to 4.99)
- 22mm or 7/8" wrench or Oxygen Sensor socket (7/8" deep well socket)
- Hammer or Mallet
- About 1 hour of time
You will need to grab one of those Spark Plug Non-Foulers you just bought.
Take one of them and brace it against something solid, you will need to drill out the rest of the non-fouler in order for the Oxygen sensor to slide inside it (approx 1/2 inch).
When drilling metal, it is best to take it slow. If able, borrow a multi-speed drill that you can control easily.
Some kind of oil will need to be applied to the metal a few times during the drilling in order to provide lubrication, if you try to drill without oil, it will dull your drill bit very quickly.
Approximate time to complete: 10-30 min Step 2
Once you've finished the drilling of the one spark plug non-fouler, you need to locate your second O2 sensor (usually right after the catalytic converter.... on my 99 civic it's basically on the underside of the cat).
Removing these things isn't easy.. and if you're lucky enough, you've had it replaced before and the mechanic didn't have a field day with his torque wrench when he put it back in.
In either case it will take some effort to get it off. I purchased a Oxygen Sensor socket (7.99 at AutoZone) and used a 2 foot metal pipe as an extender over the ratchet wrench, it gave me the torque I needed to get the thing off when a hammer and wrench just wouldn't budge it.
Approximate time to complete: 5-30 min
Now you need to screw the de-fouler onto the oxygen sensor. You want to use the one you drilled out first and simply screw it on to the sensor where it would screw into the exhaust pipe / cat converter.
Your sensor should now look like so..
Once that is complete, take the second de-fouler and screw it on, on top of the first one ....
Step 5 - Almost done
Now all you've got to do is put it back up there in the cat converter, if it's stock, you will have no problem with space restrictions and it should simply screw back in.
If you have modifications which limit the space you have, you can get an elbow joint and use a single defouler, screwed into the elbow joint, or no defouler at all.
How it works:
The principal is simple, if you allow less exhaust gases to reach the second oxygen sensor, the vehicles' computer will be tricked into thinking that the cat converter is working because of the absence of non-treated exhaust gases.