So I'm finally looking for a shop that will make me a test pipe for my car, and then I stumbled on this...



Will removing my precats on an S4 mess up the O2 sensor readings? A friend of mine mentioned that he got a check engine light after he deleted cats on his GST, and another that got a CEL after he straight piped his Mustang. Both of them said that they needed to get something that would bypass the CEL, and that their cars did not run will until they installed the bypass.



From what I understand about O2 sensors and what they do, this shouldn't be a problem; and I haven't found anything in my searching on here that mentioned anything about that happening. Is this just something that is just understood, or something that doesn't happen to RX7's?

The o2 sensor is way before the cats. I've never ran a cat on any of my rx7s and had it never set off the check engine light.

some newer vehicles throw a code specifically for the cat itself. May have been what they experienced.

Okay, that's good to hear. I guess since they were in newer cars, that's what they were experiencing. My cats will be gone!

I gutted all 3 on my old 88GXL. Never had a light come on either. Not sure if I lost or gained anything. Never really felt a difference. Wasn't even that much louder, but I still had the stock mufflers as well. Fun weekend project. Good luck! Dont get busted!

Thanks! I will do my best. https://www.nopistons.com/forums/pub...t/bigthumb.gif Cops seem to be fairly chill about loud exhaust systems here in TX. Both of my friends I previously mentioned don't get hassled much about the noise and such.



I'm working on getting a test pipe made for the main cat, so hopefully I will notice the difference. I haven't found someone who will make a test pipe for the precat though. Just need to keep searching I suppose. Anyone know a good exhaust shop in DFW?

You could just knock out the guts in the stock ones and bolt them back up. If someone did want to be nosy and look underneath the car they wouldnt know the difference unless you had to go in for a smog check and get muffler probed. Haha I said muffler probed.