O2 sensor placement before Catalytic converter

[Vdub2687]

I just changed my exhaust to a ARM catted 3 inch downpipe and I have a 420 error code. I have 3 bungs to put the sensors right after the turbo, before the cat, and right after. If I put a spacer on the one before the cat and leave one right off the turbo could i eliminate the code without having to do a tune?

 

[BudgetPhoenix]

TBH these cars especially the CBFA engine are extremely picky about the o2 spacers. I think some people have had success with one post cat, others needed one both on the 2nd and 3rd and also they are really sensitive to the flow so some people have reported only getting the codes to go off with certain types of spacers or a J-spacer with a certain jet size. There's a lot of factors and it seems like no single placement is the solution to everyone's problem. You can prob get the P0420 to go away with any combination of spacers but you'll prob start throwing 02 sensor stuck rich/lean codes so you need to play around with it. A surefire way is to get a stage 2 tune that blocks the p0420 code and run no spacers.

 

[GolNat]

I'd try a j-spacer with the smallest insert on the post cat (last one) sensor.

I'v never had any issues with the above setup but I always ran a stage 2 file. I'd get full emissions readiness according to OBD11.

 

[CleanAsFckMk6]

dont mess with or add anything to the 1st or 2nd o2 sensor. The first one monitors the air/fuel mixture and makes adjustments to keep the engine running properly and the 2nd measures pre-cat. As mentioned a stage II tune will disable the 3rd o2 monitoring. This will eliminate the CEL from popping up which is good but will also cause you to fail emissions in a lot of states bc the last o2 will never show ready.
When I need to get emissions done, I change my tune to the stock non-test pipe file a day or 2 before. That will enable the last o2 and with the j-spacer it sets readiness once I drive around alittle. Then I take the car, pass inspection and emissions w/o a problem and normally switch back to the stage II fine before I even leave the parking lot

 

[GIACUser]

dont mess with or add anything to the 1st or 2nd o2 sensor. The first one monitors the air/fuel mixture and makes adjustments to keep the engine running properly and the 2nd measures pre-cat. As mentioned a stage II tune will disable the 3rd o2 monitoring. This will eliminate the CEL from popping up which is good but will also cause you to fail emissions in a lot of states bc the last o2 will never show ready.
When I need to get emissions done, I change my tune to the stock non-test pipe file a day or 2 before. That will enable the last o2 and with the j-spacer it sets readiness once I drive around alittle. Then I take the car, pass inspection and emissions w/o a problem and normally switch back to the stage II fine before I even leave the parking lot

In my experience APR is the only tune that disables the CEL. With most any other tune you can use a spacer and pass ODBII. The system is looking to see that the cat is doing its job so it measures the difference between pre and post cat. If you take the cat out (putting in a downpipe with no cat or high flow cat) the system will of course see what is going on and report back. Using a spacer to pull the O2 sensor out of most of the exhaust stream can give you the needed reading to fool the system.

If you have a non APR tune you could do the spacer thing, and check ODBII readiness with a ross-tech cable before you go to your emissions test. Or you could switch to your stock downpipe and again check it before you go. You should clear all codes before checking.

 

[CleanAsFckMk6]

Yeah fuck changing out the downpipe just to go pass, Seeing some of the crazy things people do , just to run catless or a setup that they know doesn’t pass just doesn’t seem worth it to me.
my old mk6 gti which was fbo, with an Ultimate Racing TB, tuned by Eurodyne stg2 was great. I never had to touch a thing when I took it in and always passed easily.
My current gti is a little more of a pain, apr turboback, but even with the high flow cat as long as I put it back to the stock file a day or 2 early so I can go on a few good cycles and get the exhaust nice and hot i can always to get them all to set, which I also monitor with vcds so I know when I’m good to go. At least with APR you can quickly switch files too so I’m normally already back on the stagell file before I level pulled out of the parking lot

 

[vdubnick]

In my experience APR is the only tune that disables the CEL. With most any other tune you can use a spacer and pass ODBII. The system is looking to see that the cat is doing its job so it measures the difference between pre and post cat. If you take the cat out (putting in a downpipe with no cat or high flow cat) the system will of course see what is going on and report back. Using a spacer to pull the O2 sensor out of most of the exhaust stream can give you the needed reading to fool the system.

If you have a non APR tune you could do the spacer thing, and check ODBII readiness with a ross-tech cable before you go to your emissions test. Or you could switch to your stock downpipe and again check it before you go. You should clear all codes before checking.

Unitronic, stage 2 and above removes it as well.

 

[BudgetPhoenix]

Eurodyne disables p0420 too by default