Got my headers, HFC's and cat-back in!
 

Just installed Speed Engineering headers, Magnaflow HFC's, and a Magnaflow Street series cat-back this past weekend. When I went to start it, I was like...a little change in sound but nothing that would annoy the neighbors. I didn't get a CEL either...until after about 15 or so miles of driving. When the CEL came on, it's like a beast woke up. The sound got really deep and different. Is this normal? Will this deep tone go away if I get it tuned (hope not) or did it need to break in? I had to stop to look under my car and make sure everything was still intact since I seriously thought the cats must have slipped off the headers (used a band clamp there) but nothing looks out of the ordinary. Sorry for the noob excitement. Haven't walked down this road since my ricer days with the Honduhs. Tuning coming soon.

I went the same route with the hfc as well. I have Borla ATAK though and I had mine tuned with install. Very happy so far. Sorry I can't answer your question

I'm surprised that you didn't notice much difference to begin with, but if anything my exhaust got LOUDER with my tune. It sounded even better which was good, but it definitely didn't quiet down. Enjoy your new setup!

Same here! Granted I didn't do HFC with mine, but even with the stock catback at the time it was night and day difference when firing it back up. Didn't remotely sound like the same car!

Oh I definitely noticed it. I said I didn't think it would annoy the neighbors but after CEL came on, it got substantially louder. Wondering if anyone else noticed that when their CEL came on because of removing the rear o2 sensors?

Dn't you have your rear o2 still? You said you have HFC...so I assume you have rear sensors still? Otherwise not sure why the cats would be on there. Either way, my exhaust note didn't change once the code popped up, or at all really.

I got a CEL almost immediately on mine, but I just used their midpipes and didn't have cats or rear o2 sensors..so I was expecting it. They sell cheap little bluetooth OBD2 readers you could use to make sure the CEL is related to the exhaust.

Also, be warned if not running o2 sensors...you need to tune it pdq or you run the risk of the code(s) getting set to permanent, and will still throw engine light even after being tuned out with something like HP tuners (ask me how I know :( )

Thanks for the heads up. In my research, a lot of guys were saying it would be ok to run without a tune for a while and all it does is make the car run rich. Looks like I'll be hitting up Dynosteve a little sooner than expected. To answer your question, no...I do not have the rear o2 sensors because the cats didn't have o2 bungs (Magnaflow part# 59959) and since I was going to get it tuned out anyways, didn't bother to have bungs welded on.

I’m surprised that they didn’t have O2 bungs. I was always under the impression that with cats the O2 sensors still played a part in the system even though the flow is substantially higher than with the factory cats.

Have you tried the universal trip drive pattern to clear it?

https://www.autoserviceworld.com/fea...ermanent-dtcs/
I'm sure LT set like SP or TSP, who have their own cats come with bungs and flanges. I out sourced mine as SE doesn't offer cats so I went with universal Magnaflow cats.

The rear o2's are only there to determine if the cats are doing their job. A set of high flow cats won't filter as much as stock so they're tuned out to avoid the cat efficiency codes

It is "ok" in the sense you aren't gonna hurt the engine. It does just run a bit rich. But after 2009, GM vehicles have some codes that can set as permanent and the only way to clear them is to correct the problem. Luckily only my o2 heated circuit codes had thrown. I just plugged my rear o2 sensors in and it cleared. And since those codes are tuned out, NOW they won't set a CEL

If your catalyst codes set, the only way to get rid of the CEL would be to have cats and rear o2 sensors that all functioned to clear the code.

My tuner said he has a client with this issue. No cats and his CEL keeps coming on, even though it should be tuned out. Didn't seem to be a ton of info about this when I searched. But I ran hundreds of miles untuned and the engine wasn't any worse off for it