So I just installed a set of long-tube headers on my truck.

>4 o2 sensors

Wut?

File: IMG_0666.jpg (1MB, 3264x2448px) Image search: [Google]

1MB, 3264x2448px

>>15336434

Not OP but my LS3 stock manifolds had 4 sensors, 2 primaries and 2 secondaries

OP, you're gonna need a tune with longtubes. Even long tubes with high flows will throw a CEL, at least on my car there is no way around this. A tune should take care of everything

File: 2010-01-05_214420_1.gif (15KB, 544x350px) Image search: [Google]

15KB, 544x350px

>>15336434

2 upstream
2 downstream

>>15336444

I figured that was the answer even though I really didn't want it to be.
Got a general ballpark for the price of a tune?
I'm living in the South East US if that helps.

>>15336459

Where at specifically?

SCT X4's are decent and run around $400 after taxes. You could also get a mail order tune from a local shop depending on how close you are. I got a email tune from PCM of NC because I work literally 3 miles from the place so I just showed up to let them read my ECU and then came back the next day to have the tune installed.

Would've gotten a dyno tune but they're booked till fucking October lol. You're probably gonna need an auto trans tune too so idk you'll have to search around on that one.

>not hearing or feeling anything different
>could be the cats or o2 sensors
no you would definetly feel the difference in driving if your cats were shit noob.
also,
>having more than one catalytic converter
stay pleb american car owners.

>>15336477

I'm in central NC as well, just a bit strapped for cash atm.

>>15336497

PCM of NC charges $250 for an email tune. You don't gotta send off your ECU if you can just drop by during their shop hours around 12PM after filling out an order sheet. Their laptops are on the dyno all day so around lunch time a guy named Mark at the front desk can hook you up.

They're great to work with, probably the most renowned LS shop in the state

The advise in this thread is horrible. Buy a few defoulers at your local auto shop. Problem solved.

>>15336527

>the advise in this thread is horrible

Nah you just have no experience with GM V8's eurocuck

Long tubes/high flow cats will throw codes no matter how well your sensors are functioning. It needs a tune.

>>15336423
Usually altering your exhaust system in any way is going to fuck with your computers feedback from the O2 sensors.
potentially the erroneous downstream feedback can be considered negligible but the upstream feedback is going to fuck with your shit

>>15336567
Nah you just have no experience with using a defouler. Or cars for that matter.

Try the defouler OP.. Might as well spend $10 and see if it works before spending hundreds on a tune.

>>15336423
>cut both of my front cats off and am now running with just both the rear cats.
yeah, your ECM definitely aint gonna like what your O2 sensors feedback from that arrangement.
Do you have access to a handheld diagnostic to get the actual Check Engine Fault code?
pretty much guaranteed to be an O2 sensor fault reading of some kind, but would be interesting to know the exact code

>>15336614
>>15336594

How do I defouler?
Also, I don't have a diagnostic tool, anyplace that can do, let me use one for cheap/free?

>>15336660
>diagnostic tool
there are phone apps for diagnostic tools. literally download it for free or maybe just a few bucks. probably need some kind of adapter plug is though.

File: 9a_v6_35.jpg (93KB, 900x675px) Image search: [Google]

93KB, 900x675px

>>15336660
A defouler is a hollow extension designed for 02 sensors. Used when a secondary 02 sensor is throwing a code.
As long as it isn't your primary 02 sensor (the one before your cats) these will usually work.

>>15336717

I'm gonna guess I can just go down to a parts store and grab one of these?
Not even in an emission test state but I seems sketchy enough to not have them on store shelves.

>>15336423
Sensors measure the emissions before and after cat. If you removed the cat but kept the sensors the two o2 sensors would give you the same reading and it will give you an error because it thinks your (non-existent) cat is failing

https://www.youtube.com/watch?v=qHD7T7EhuzI

This will fix it. Skip to 2 minutes in

>>15336717
You can also buy these with a little mini cat built in, to trick your Oxy sensor and run no cats

>>15337360
yeah that's a """fix""" the same way patching up rust hole with duct tape is a fix

>>15337512

What do you recommend?

>>15337306
Yeah most auto stores sell them. Autozone, o'rileys, pep boys ect.

>>15336567
Except it actually doesn't lol. Op needs defoulers two or three long and then screw the 02 on. I've done it on every car I've ever owned and for friends car. It's a simple fix that you think you need a tune for. If he wants more power then a tune would be great but he simply wants the cel off. Don't give him shit information when you doing know what you're talking about

>>15337487
It's not a cat it's a charcoal filter

>>15337512
You're an idiot and have no idea how those systems work clearly

>>15336423
>I got a check engine light

Use software.

>>15336423
Remove instrument cluster, take out bulb. Put cluster into original position... and no more CEL.
Cheapest fix ever.

File: 12.jpg (38KB, 600x450px) Image search: [Google]

38KB, 600x450px

>>15336423
You need to install a spark plug non-fouler over your o2 sensor.

Without a cat, the sensor has too too much air flowing over it, and is getting the wrong readings.

I had the same issue in my Civic when I replaced my CARB certified $800 cat with a cheapo Magnaflow $50 cat.

Sometimes you may need to use 2 as in pic related. This is guaranteed to solve your issue.
Shit son, you even posted an image with the setup I'm recommending.

>>15341783
This
But you may also need to add a filter to the sensor output to extra fool the ecu.

Same scenario as OP, but no Cats and rear O2s were previously turned off. PCM failed and had to get a new one and did not have the existing tune. Inspection is coming up and I was wondering if the defouler trick would work. I am getting conflicting reports. It's for a 2006 Pontiac GTO.

>>15336423
>I just installed a set of long-tube headers
Do you notice any performance improvement?

>>15336423
>I cut both of my front cats off
If you are not in a smog state, why care about the CEL?

>>15336660
If you live by autozone they will give you a free diagnostic

File: download (1).jpg (8KB, 259x194px) Image search: [Google]

8KB, 259x194px

Ok so first off those defoulers work sometimes but I've never had much luck with them on gm v8s. Most tuners I know just delete the post cat monitor in those cars. Diablo sport programmers can also do this. You bought longtime so obviously you're spending money on the car, do it right and fix it with programming. It's the only sure fix.

>>15336459
Sparkplug defoulers. Did the same mods on my buddys gt mustang and the plug defoulers have kept the cel off so far

>>15336423
Holy fuck this thread.
Mil eliminator op.
Plug into where the upstream o2's were, problem fixed.
Jesus, we've been doing this for 25 years now...

>>15336527
This

>no dude you need a tune bro!
Where do people come up with this shit?