I'm trying to modify my header so that the O2 sensor doesn't throw a code(P0421).Does anybody know what size spark plug anti fouler i should buy for a 2004 Eclipse GS 2.4l? Thanks for your help.

There are short ones and long ones , visit the help section of yur local parts house. I did nt have a non fouler on hand but this is wut i was trying to explain in teh other post wut yur spossed to do to the side of the non fouler screwing into the exhaust pipe so the tip of the HO2 sensor can be slightlly in teh exhaust stream if its a short non founler , there are longer ones also.

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Will any size(Long or Short) fit into the O2 sensor hole on the header?

The correct way is to extend your o2 sensor and place them in the correct spot.

How would I go about extending my O2 sensor?

Cut wire, add wire. Extension complete.

Its not really about moving it to another location. The fault he has is with his oxygen sensor located before the catalytic converter , the one where on teh original exhaust manifold it was higher on the collector pipe. The O2 sensor trick is used mainlly on the rear HO2 sensor located after the catalytic converter , the thing is when using a higher flow catalytic converter , the rear HO2 sensor will accumalate a higher range of heat due to the higher flow of air at lower rpm's which is higher than the stock variable limits. The HO2 sensor trick moves the sensor , depending on the non fouler used, out of the high flow of hot exhaust air , bringing a lower stream of air directed at the HO2 sensor bringing it back to a stock sensor range.

The problem is that with his sensor before the catalytic converter is that is i am correct by the code that he said he was showing up , is that its not getting enough heat. The old manifold the sensor sat flush in the manifold putting the tip of the sensor directly in the stream of air . But the fitting that is welded into the headers down pipe is not allowing the HO2 sensor to be far enough in the stream of air.

Which is why SC Customs said he needed to extend the O2 sensor.

Extend to where????? Yu can extend all yu want by adding wire. That wont help the element part of the sensor frum being farther inside of the exhaust system. e are not talking about extending it farther down the exhaust system , the element needs to be farther INSIDE the exhaust area. Ive put up a badly drawn bitmap that should illustrate my point.

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Yes, I'm referring to extending the wires so you can re-route the o2 sensor to be at another point in the exhaust system (farther down). Jesus - I didn't think it would have to be spoonfed.

When you remove the OEM manifolds and pre-cats and install a header (or headers) depending on I4 or V6, you are removing those pre-cats. The sensor(s) that used to be before the precat you relocate to be just before a HFC after the collector pipes. The sensor(s) that were after the pre-cat, you relocate to after the HFC.

If that works for yu . Ive never had to extend or rewire anything , All i do is shorten the fitting thats welded in the header for the sensor to screw into , thats it. And screw the sensor in and it screws flush , sensor head sits farther inside, in exhaust stream and problem corrected. But if adding wires and welding in another fitting to put the HO2 sensor in a new place farther downstream then good job.

How do you shorten the fitting?

It's not what works for me, it's what works for the vehicle and for emissions. I only OWN a shop and know WTF I'm talking about, so thanks for playing.

Blox makes something for that i heard it should be universal it will clear any CELS

Would an Exhaust shop be able to relocate my O2 sensors? I don't have any experience with welding so I would probably need someone to do it for me. I tried to do that anti fouler mod but I can't get drill the hole big enough for my O2 sensor to fit without messing up the threads on the inside of the anti fouler. If anybody has successfully done the antifouler mod to a 2.4l 3g eclipse, please let me know how you did it. I think I'm going to have to do what SC Customs said and move the O2 sensers to another spot. Thanks for your help in advance.

Yes an exhaust shop will be able to do it for you.