Take a quick look at my post here, it has alot of info:
http://forums.vwvortex.com/showthrea...1#post77719864
When you add a larger Diameter DownPipe you have changed how the car breathes. Your PRE-CAT Sensor will read higher with a larger DP. Also, on the CBFA motors they have two sensors as they run cleaner, they are detecting the PRE CAT o2 VS Post CAT o2 constantly, and it needs to satisfy certain criteria to not throw a CEL.
This is why i don't like the test pipe file, many people have it not really knowing that their car is truly throwing a CEL and not going to pass an emissions inspection.
As stated above, I would buy two RAI J spacers, they will allow you the best amount of fine tuning with their Jets. Some have been able to run CEL free with ONE SPACER on a CBFA but IMO its best to buy two and have them ready, since they are not really very pricey.
Just because one spacer does not throw a CEL right away, does not mean a year later you dont start throwing CELs again, these motors are finiky and even stock setups can throw a CEL at times. So having two adjustable J spacers makes good sense.
