CEL on WRX...weird story (I think)

[WRXtreme]

I just had a very strange thing happen to me. I was getting a CEL after I
removed all three cats from my car and kept the stock exhaust. This light
came on every 3/4 of a tank of gas and would stay on for about 50 miles or
so. Now I have upgraded (a couple of weeks ago) to an Apex-i N1 Exhaust and
haven't had a check engine light since. Anyone care to try and explain
how/why that would happen? Is it possible the stock exhaust is so
restrictive that it messed with the O2 sensor and triggered a CEL (I am
positive that it is the O2 sensor that caused the CEL, had a scan tool
analyze that)? Anyone else have anything like this happen to them?

CAS

 

[JaySee]

Boo! Gross polluter.
You should at least keep the 3rd exhaust after the turbo or replace it
with a high flow. 5-10 less horsepower, but WAY less pollution.

 

[WRXtreme]

I live in a non CARB state, but I do have access to a meter that shows how
much smog/pollution I am putting into the air, I rate better w/o the cats on
this car than I did when I owned a 96 Neon with cats.

CAS

 

[Jeff]

The cat in the downpipe is the same used on the worldwide STi, it is
supposedly good to 300 Hp. No need to remove it. The cat before the turbo
can be replaced with an straight through uppipe. On the Perrin version, you
remove the temp sensor (not an 02 sensor)on the oem cat and use a Perrin
supplied resistor to avoid the CEL. The third cat can also be replaced by a
straight through design which has a place for the O2 sensor. Jeff