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Hey guys,

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

Tools Needed:

- 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



Step 1

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




Step 3

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 ....

Like so....



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.

 
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Update... This method worked for about 10,000 miles but once I hit 290,000, CEL popped back on for o2 sensor, just reset everything by disconnecting the battery and it's been off for over a thousand miles now

 
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you should note that this is illegal in some state especially regarding passing emissions.

but good work... half the things on my car are illegal so who am i to judge? haha

 
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lol you're right. it is illegal in most cases, but most the time unless you're in some ridiculous state like new jersey, they don't care that much... or really they don't even check, they just check if your CEL is on for anything..

Luckily I live in a county that doesn't require emissions inspections, although most of the rest of the state does.

 
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When I look under my 2000 civic I see the one closest to the front of the car looks like its on the top end of the catalytic convertor?

is this the one causing the same check engine code?

please let me know. ordered the defoulers, got them today.


thanks all

 
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Second O2 sensor on underside of cat, got the socket on it and what do ya know? cant get a rachet in there to turn it, not enough room. what do i do?

 
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[quote=dkablack;4474154]Hey guys,

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

Gonna do this ASAP. Thanks for the write up

 
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This worked long enough for me to pass inspection and not have to change the catalytic converters. I successfully eliminated codes P0431 and P0421 for a bit but the "check engine light" came back on a little while after I got my inspection.

My experience is as follows:

Cost of DIY (for 2003 Mitsubishi Montero Sport):

Two Sets of Non Foulers: $12 bucks as I have two O2 sensors after the catalytic converters(s).

Three 1/2" Drill Bits: About $45 (I had a lot of problems drilling out the non foulers. I went thru three drill bits). This was a pain.

Time to Complete in Total: 5 hours. Why?

(1) You have to remove the rear Cat O2 sensors....not so easy. Then you have to drill out the non-foulers....I wasted a lot of time on this and went thru three drill bits. I don't care what anyone says....this was a pain.

(2) Putting the O2 sensors back in was difficult. For one of the O2 sensors, I could only get in one spacer (due to space restriction) and was lucky in getting that one back in....I almost gave up. The fact I was only able to get one spacer in for one sensor is probably the reason I obtained the dreaded P0431/P0421 code again.

Was it worth it? I am going to cautiously say yes for now... though I think it will work for a longer period if I can get the second spacer on the second rear O2 sensor. I initially was looking at having to replace two catalytic converters in order to pass inspection which would have cost me about $2000 dollars at the dealership. So I am happy it lasted long enough for me to pass inspection, get my registration and avoid a hefty ticket fine for not driving an inspected vehicle or a vehicle without a registration. You see in my state, you need to have a valid inspection before you can get your license plate registration. You also have to pay vehicle property taxes but that's another story. Anyway, I have some more time now and I am going to find a way to install the second spacer and try to provide an update later on how it worked. I also plan to run a lot of fuel injector cleaner thru my fuel system and use premium gas as I understand clogged fuel injectors can also result in unburned fuel and poor catalytic converter performance.

Afterthoughts: I originally probably fouled my catalytic converters since I failed to replace a bad "upstream" catalytic converter oxygen sensor for about a year. The upstream Cat O2 sensors are important in that they control the air/fuel ratio according to my understanding (thus this trick of using non foulers is only to be used for the O2 sensor after the catalytic converters which cause errors P0421 and P0431). The bad upstream O2 sensor probably screwed up the air/fuel ratio causing a rich mixture which I suspect I deposited a lot of carbon on the converters causing them to not work as efficiently. Anyway, the car I have has 106k miles on it and I am not about to "waste" money on new converters to meet some emission standards. For information, failure of the upsteam O2 sensor causes a different fault code. Thus my first step in getting this fixed was to replace the upstream cat O2 sensor.

 
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Using Two "Spark plug Non fouler" is wrong, you will end up with the MIL light back on, because the ECM will detect that the O2 sensor is inactive.
it is equivalent to plugging the o2 sensor hole with a plug while leaving the o2 sensor attached to the harness.

you will get code P0154 " O2 sensor circuit No activity detected."

therefore I think that the use of the second non fouler is the problem, it keeps the O2 sensor cold enough to trigger the Fault code, specially if you have a car where the downstream O2 sensor is exposed to a lots of cold air, such as engines that have front exhaust manifold.

the solution is to only use one Non Fouler that way the O2 sensor will get exposed to more heat and still covered and not exposed to the bad gases.

try it and leave your feed back. let me know if it works out for you and share the knowledge

 
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hey guys..

i installed after market header 4-2-1 on my 1999 civic cx hatch and i also installed 2 non fouler spark plugs on my second 02 sensor and it works like a charm(no CEL yet).

im worried now about my rubber boot in my CV axle, because the second 02 sensor is touching the rubber boot of my cv axle and it might broke it. is there any elbow connector that i can put the sensor in so that it will be away from the rubber boot..

thanks!

 
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I used 2 de-foulers... 50,000 miles later.. still no check engine light.. but it will turn on if i disconnect one of the wires to the MAF? air sensor in the air box.. so i know it's not just burnt out

 
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there are elbow pieces.. i've heard of people installing these as well to get some clearance around pipes underneath.. you're just tricking the thing into thinking that the air is cleaner.. they don't seem to malfunction as much as the previous posted had stated when there is too little exhaust getting to them.

 
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Just did this on my civic and two days later CEL poped up for a p0137. O2 sensor is brand new. My cat is completly shot It rattles like crazy due to the broken internals but I wanted to get rid of the CEL till I bought an aftermarket one. Could this be causing the CEL?

 
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Almost everyone says replace the cat, but almost never anyone says to try and clean the cat, here is a link I found that might save you a fee hundred dollars, or might cost you a few dollars more if your cat is in unrepairable condition. But i think its worth a try to spend a few bucks in atempt to save a A few hundred. i have this code and I will give it a try this week and see if it works

 
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Thanks for the pics and videos.

 
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hi guys new to this I heard that their a way to get rid of my 2 o2 sensor if I loop the wires my cat is bad got a new exhaust system new one came with a pipe no cat so no o2 sensor hole have you guys heard of doing the wire loop

 
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Can you help paste a link of the video

 
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I doubt he'll see your message since he hasn't logged onto this site in almost 8 years.

However, there's really not much to it. The Dorman part number is still good to go, can find it at any AutoZone or similar. Drill one non-fouler out (enough that the O2 sensor can pass through it - 1/2" drill bit works perfectly), screw that into the untouched non-fouler, screw the O2 sensor into the non-fouler assembly you just made, install it like it was a super long O2 sensor. That O2 sensor socket is stupid helpful, but not necessary. Make sure you only do it to the post-cat O2 sensor.

 
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I only used one non-fouler on a 99 worked fine