Liner

Hi! Installed catted headers and followed several of the install threads on the forum. I ultimately plugged and DID NOT install rear 02s despite several conflicting opinions in threads such as this one:

http://forums.corvetteforum.com/c6-t...tallation.html

I'm trying to do a custom tune with Lew, and I keep popping codes for all kinds of things, including rear 02s. I know you can tune the rear 02s out, but do you NEED to have them connected to manage the heat in the cats and avoid burning them up? (or is there another reason to hook them up?)

Putting them in now is obviously a hassle as they are tough to get to, but I want to do this correctly and obviously not harm the car.

The few miles I've put on the headers have performed great and I love them. I just want the codes gone and the catted headers functioning correctly.

Thanks in advance!

AzMotorhead

Only thing the rear O2's do is report the condition of the cats.
Just delete the programming(turn them off)

ls1121

NEED to have them connected to manage the heat in the cats and avoid burning them up? (or is there another reason to hook them up?)


manage the heat? never heard of such a thing. Your Tuner should have answered all of your questions already, if not I would search for a new tuner.

Liner

I was paraphrasing, but here is what I was told:

"rear O2 sensors should still be installed in the pipe and connected to their wiring harnesses... those monitor the cat performance, so if they get too hot, they tell the pcm to add more fuel to cool them down, otherwise you'll burn 'em up..."

rabrooks

Plug them and do a tune to turn them off. If the cats get too hot, I suppose they'll burn out. Then you can take them off and gut them, and re-install them. But that will probably cause a need to re-tune. Mine are off and I have no issues and I track the car. My cats are LG high flows. That may make a difference.

Larry Myers

When my shop/tuner installed headers and mid pipe with cats he installed the aft O2 sensors and then promptly turned them off. In two years have had zero problems.

Liner

Well, I think I'm going to try to add the rear 02s. Tuner already gave me a tune for when I get them on.
Anyone have any advice on how to do this (without taking the exhaust apart or off the car)? I can't even see the connections! Actually, I think I can see the driver's side, but I don't think I can reach it. Can't find the passenger side...

Joe_G

The rear 02's are for emission purposes only. If I was you I'd turn off the P0420-430 codes and not fool with taking your headers down to install them. By turning them off in the tune (which is what virtually everyone with headers does with zero problems) there is no reason to go through the headache of installing them.

C7/Z06 Man

I installed two electrical extensions with the anti-plug fouler "fix" ($10) in my 3" catless X-pipe that had bungs for the two rear 02 sensors. I have driven and raced the car for many thousands of miles now with no codes on the " OEM STOCK" or a canned "Intune" tune. NO CODES EITHER WAY AND NOTHING TURNED OFF IN THE TUNES.

Just letting anyone that may want to try this approach of what my results have been.

Oh, and the DiabloSport "Intune" canned tune along with my mods has propelled me to the top of the Grand Sport 1/4 mile bolt-on list "AND" I also kick a$$ on "all" the lighter narrow/standard body LS3s that are running the "same" type of "bolt-ons" last time I checked.

SUB VETTE

I installed my rears with wiring extentions and then the tuner turned them off. I was under the impression that they needed to be there and hooked up so electrical continuity was established allowing the computer to recognize their existence before they could be turned off.

ls1121

except maybe that gaping hole in the pipe?

Joe_G

Let's hope he plugged the holes with plugs when installing the headers.

Liner

Yeah, they are plugged.
The problem is that my cats are overheating. I can smell them burning when I park the car. The rear 02s would monitor this and fuel would be adjusted to keep them cooler. That's what the tuner says and it makes sense. I think many of the people running without rear 02s are running catless. I'd rather not fry my cats (and have people ask me "what's that smell" every time I park), so I'm going to hook the rear 02s back up (unless Grand Sport Man's fix will work. gonna pm him).
It's not about "just tuning them out", they're throwing codes because my cats are cooking!

AzMotorhead

Because you're throwing too much fuel or timing at the motor.
Cats are designed to burn off excessive HC's
Hydrocarbons( unburnt fuel). They're doing their job as best they can you're just overloading them

ls1121

Your front sensors are what adjust the fuel mix. I had them (rears) tuned out on my Z28 years ago with no issues. When I take my Vette in for a Tune I'm sure they will be off also. Rear sensors tell the computer when the Cats are bad or going bad, It's a pollution control thing.

I've never heard of them being fried, clogged or broken and falling apart inside but never fried.

Liner

Just FYI for the forum... Here is the explanation I received:

The FRONT O2 sensors are the ones that control the fueling/fuel trims.. if you're running lean or rich, the FRONT o2 sensors report the data to the ecm and the ecm adds or subtracts fuel to keep the stoich AFR at 14.7 for part-throttle fueling/regular driving...

COT is Catalytic Over-Temp protection.. The REAR O2's detect how the cats are working.. COT is, if the cat temp gets too high, it tells the ecm to add more fuel, richen it up, to cool the cats down... the REAR 02's are to monitor how the cats are performing.. and I say you SHOULD have the rear O2's installed, because you DO still have cats on the car... so the cats can be monitored correctly...

A tune will not prevent you from burning them up.. because the rear O2's and COT is disabled, because you removed the rear O2 sensors...

Guinzu

So since you don't have rear O2s, how do you know they are burning up? You did say there was a smell, did you buy the headers/cats new? I remember hearing something about new stuff having a smell for a short period.

Liner

So, just thought I'd close this thread out and hopefully it helps someone down the road...

I did install the rear O2s. It was a pain -- they're very hard to reach with the headers in place, but I got to the one on the driver's side relatively easy from underneath, and my daughter (with her small hands) was able to reach and do the passenger side from up top -- she was really proud of herself and I took her to DQ as a thanks

I installed the tune for all four O2s installed and everything is now right with the world. No codes. Runs great.

So, it is my belief that catted headers need all O2s installed to run correctly and not throw codes -- As sub vette said, they need to be there to be tuned out.

Like I said, I hope this helps others down the road...