What I don't understand is why you would even consider running your wideband after a cat!!! Everyone here has admitted that a cat does change readings, infact they HAVE to. Converters are in place to burn off excess hydrocarbons and convert carbon monoxide, The byproducts are water vapor and carbon dioxide. That's my .02 Hey alvin, you the guy from pcmforless?
05 colorado 8lbs boost
89 427w 'stang
I moved mine to the post-cat location due to a leak in the driver side collector. I didn't have a spot to weld in a new bung on the passenger side pre-cat. It'll move it back to the driver side pre-cat when I get new headers. I'm content with the minimal deviation in my data, though.
looks like the car is already tuned tho ... nice to see a chart
and wondering if a less tuned ( rich or lean ) would show a more exaggerated diff ??
yes i wondered if thats the "alvin: too ..?
sorta boggles my mind arguing if cat makes diff.....everything i've READ says it will and ??????....... a bung precat was not hard compared to the rest envolved in this process
not to say "going to a shop " for something simple does not have its own inherrent issues......................
2.4 ecotech ( 2006 pontiac solstice )
42lb injectors
trim 50 garrett t3t4 (custom -barebones pumpking )
boost @ aprox 7 <10
38mm tial wastegate and bov
3" tubes front to back
werks radiator
bell intercooler
GXP,magna flo exhaust-with integrated dumptube by B_FASTER & R&D
aem wideband
custom manifold -by sh**er the skunk
(((HP ))) tuning -in progress
jet hot 2000
aerospace logic egt kit
If there is no/very little O2 in the exhaust(after-cat) at WOT(or any time, really...that's the cat's job is to use the O2 to break down the other toxins) then the O2 sensor WILL read rich compared to pre-cat, wouldn't it? Since O2 sensor measure O2? But the cat is only going to use whatever O2 it needs to break down the other toxins....so there is still plenty of O2 in the exhaust after-cat, but the reading is not going to be as accurate.Originally Posted by Alvin
But actually, there IS a lot of O2 in the exhaust.....hence tuning for (ex 12.5 afr....) 12.5 parts O2 to 1 part fuel. You will have a truer reading pre-cat versus after-cat.
I just found this thread, thanks alot for the graph. Nice to see the differences.
Old post, just saw it, recently went hunting for a new sensor myself.
Best price I found was on Amazon, free shipping too.
Search there for Bosch 17014.
Wow, first time I visited this thread in a very long time.
You guys have a very wrong idea of O2 left over in a rich mixture
There is no left over O2 in a rich mixture, that is why it is a rich mixture. The only o2 that can possibly be left is that which is occurring as a result of combustion inefficiency.
So, if there is no O2 left in the exhaust, there is no way any more "burning" by the cat can take place. Try keeping a match going underneath a glass.
Tuner at PCMofnc.com
Email tuning!!!, Mail order, Dyno tuning, Performance Parts, Electric Fan Kits, 4l80e swap harnesses, 6l80 -> 4l80e conversion harnesses, Installs
you need to multiply your % numbers by 100 to be correct.
Oxygen sensors don't just measure oxygen. They measure fuel and other gases as well.
Post cat can make a difference. I hate doing post cat, and try not to. Plus the lag. At the tailpipe-some shops do it because it's easy. But the instructions for the different adapters often state short exhaust and no cats.
Stock cars may not be in much danger, but some of the more radical setups...why chance it?
I agree, threw me off at first
Old thread I know...
My comment is in reference to measuring at the tailpipe as mentioned above.
I ROUTINELY run cars in OL with a WB in a front bung and I also use the tailpipe wideband on the dyno. I use it because it is there. The tailpipe pickup for the DJ almost without fail reads 0.5 leaner (AFR) than the one at the front EVEN IN THE CARS WITH NO CATS. I don't know where it comes from exactly, but I have seen it over 100 times easily. I suspect that is why so many dyno graphs are showing a 13.0 target being 'best'. I find that 12.6ish on my front wideband GENERALLY makes the most for N/A (though of course each one is a little different), and leaves the DJ AFR printout at 13.0-13.1.
Just relating experience...
and the 'old threads' still contain GREAT info for us beginners who are just starting to approach the wb install and all that goes along with that.
Thank you for this information. What a find for me.
Jim
Talk About NEWBIES !!!
I'm gonna go on a limb here and state that it's because of how close the sensor is to outside air. Some is in the tailpipe, whether you like it or not lol. Thus the leaner readings.
I'm new and still trying to understand wideband location. I can understand the lag from the wideband being in the tailpipe but is that an issue if you put the wideband in the rear O2 bung which is about 5 inches from the cats? Would it be worth the difference to have a bung put in front of the cats and if so, where is the ideal location.
My car is a 2009 G8 GXP with the LS3 motor. I have ARH long tube headers and their catted X-pipe with the stock mufflers. I'll post a picture of the exhaust if someone needs it. Thanks.
Last edited by 99LS1SS; 07-31-2009 at 06:50 PM.
If you are tuning (not just a monitoring WB) just pop out a front O2 and use his bung for your wideband.
Resurrecting an older thread here since I have a related question. Is there any adjustment/calibration needed or available on a DynoJet for the O2 sniffer? The reason I ask is that on a recent trip to the dyno (a DynoJet with the O2 sniffer in the tailpipe) with the car just rolling - the DJ O2 was showing 15-16 some times and 12 at others. With the car just rolling (not at WOT), shouldn't it show somewhere around 14.6?
There doesn't seem to be enough exhaust volume at anywhere except for WOT for most tail pipe widebands. As I said before, I use a wideband in a front header/manifold and usually throw the dyno wideband in the tailpipe as well since it is there. The one in the tailpipe commonly reads full lean at idle but comes back somewhat in line with the front sensor as exhaust volume increases.
That makes sense - thanks Frost!
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