2002 GMC Sierra 4.8 Vortec o2 sensor help?

**Ty_Kruszka** · 07-29-2012, 01:13 PM

I have been reading posts on here that say if I remove my catalytic converters, which i have 2 of, I will have to get an o2 sensor "tune" in order to shut off my CEL. Basically the only thing I want at this point is a louder bottom end. My exhaust is currently the stock exhaust, simply cut off right before the muffler. In order to not damage anything, I would like to replace my stock cats with simple 2 3/4" exhaust pipe, and then run a pipe from where its cut off, straight out the back. Where/how would i go about doing this o2 tune? Please do not post to tell me to keep my cats on for ethical reasons. They are coming off.

**Ty_Kruszka** · 07-29-2012, 01:16 PM

Even if I have to throw a thrush welded or a glass pack on there to boost my back pressure, i don't mind. Theres a certain V8 sound that modern trucks just don't get because of these damn cats.

**dpeter** · 07-29-2012, 02:36 PM

I do not think it would matter if the sensors are before the cats but no matter what, if the CEL does come on, then a peice of electric tape should be an OK fix for you.

**Ty_Kruszka** · 07-29-2012, 11:40 PM

I have both upstream and downstream o2 sensors, therefore the light would come on no matter what.

**CowsPatoot** · 08-02-2012, 03:29 AM

http://www.gmtuners.com/ <--- Ryan could remove those codes for you. We use him pretty consistently for engine swaps in Fieros and he does great work. I can't quote you a price, but if I remember correctly he tuned a 1998 Chevy Venture ECM for a 3400 swap for me (including removing all the unnecessary codes) for about $80. You would have to send him your ECM. Let him know if you want any other changes while he has it (does your speedo read correctly? Wanna remove the 100mph limit?) The alternative would be to find someone local that can do the tuning. Where in Michigan are you? I know someone in Flint that might be willing to do it...no clue what he would charge though.

**Ty_Kruszka** · 08-02-2012, 10:48 PM

I'm on the west coast, just north of Ludington. Flint is kind of a far stretch, but if i can't find anyone around here i would probably do it. i'd remove the limit and i assume my speedo reads right.. what else could be altered?

**CowsPatoot** · 08-02-2012, 11:47 PM

Doing anything to increase power would require scanned data...plus those kind of customizations cause the price to jump quickly (mainly because they usually require several attempts to get perfected. But I know he can also change shift points and/or firmness of the tranny fairly easily. Really not sure what all he can do that would be of interest to a mostly stock truck without getting into a full custom performance tune.

For the 3400 he tuned for me, he started with a 1998 Venture ECM, installed a 2005 Grand Am stock tune, then pulled out all the auto tranny info (I am running a manual), pulled out the VAT (security system), set a custom rev limit, removed the speed limit, and altered the VSS (speed sensor) to match my tranny. I am running an essentially stock 2005 3400 V6 with a manual 5 speed. It has full emissions (he offered to remove that as well, but I need it for inspection here in NC) with 2005 standards and runs OBD2 in a 1985 Fiero GT. The only modification to the engine is a custom exhaust from the stock manifolds back...total exhaust length is about 48" manifold to tip (the Fiero is mid engine).

Most other people that can tune a GM OBD2 ECM can do the same things, and probably for similar prices. I use Ryan because I trust him, and he is very familiar with installs into Fieros.

**rileyjr16** · 08-03-2012, 04:05 AM

My brother wanted to take his cats completely out of the equasion until he figured he could do it by himself for MUCH cheaper.

He cut the downstream pipe off and undid the cats from the flange. There he punched through them from the downstream side completely leaving nothing inside of them. After he did it, he welded a spacer onto the exhaust pipe and welded the threaded bung to the spacer. In doing this he moved the O2 sensor farther out from the exhaust gases which in turn, shut off his CEL.

My cats are gutted by a retard who didn't know what he was doing who cut a 2x3 square in the underside of the cats, gutted them, and half arsed welded a new piece of metal over the holes. To this day, I have never figured as to why I never get a code for the O2 sensors...I had Glasspacks on there and it was WAY too loud for me, mostly because they were right under the passenger seat to where I couldn't hear a damn thing; but to each his/her own.