Rear 02 sensor + catalytic converter = CEL on s14...help!

[MarkEmark]

Hey

I have a catco high flow catalytic converter with the rear 02 sensor (s14 OBD2) AFTER the outlet of the cat, and the EGR tube running into the catalytic converter too.

My question is: When I'm running a straight test pipe in place of the cat with the same 02 sensor screwed in, I don't get any check-engine lights.

When I put my cat back in (which i need to do for emissions), and put the same 02 sensor after the outlet of my cat, I do get a CEL. When the test pipe is in there, the EGR tube is unplugged and just dumps out.

Why would the CEL come on when the 02 sensor is installed in the cat, but not in the test pipe?

Can anyone help?

[yellow_jacket]

What code is it throwing? Maybe you damaged the O2 sensor when you took it out?

[MarkEmark]

Don't know the exact code, but it's the one for the "rear 02 sensor" Definitely didn't damage the 02 sensor either, as it's done this a couple of times already...

I don't care at all except that I need to get my baby smogged tomorrow !