Bad O2 sensors?

[Stormo]

Got a P0420 code, had it for a while as I tried running some cat cleaner through it. However I don't think my cats are actually bad.
I dont have any bad smells, excessive smoke or weird feelings from the engine. And it runs a hell of a lot better with the code cleared than with it there.
I decided to check my O2 sensors, and run a graph for a minute, here's the results:


Carvana techs are horrible, while they did replace a lot on the car, just simple maintenance stuff. They did mess up some stuff, though I fixed most of it.

Previous owner supercharged it, and I thought it was just a tune causing the code to trip, but the sensors look bad in my opinion as bank 2 looks fine to my newbie eyes, and bank 1 just looks all over the place. Which makes no sense.

I plan to try to swap the sensors over to the other bank and vice versa to see if the issue moves with it, however I don't have jackstands yet, and car is too low for my ramps.

What should my plan of attack be?

[gtstorey]

I don't know that you can tell from that. The computer is likely seeing the same thing but how do you know if it's a bad o2 or bad cat from that? If either sensor is bad on bank 1, I would guess that it is Sensor 1 but I wouldn't expect it to show correct mixture if the cat is partially clogged or damaged.

[Stormo]

I have a good feeling it isn't the cats because I don't smell anything that points to the cat. Car doesn't feel funny without it, if anything it feels worse with the code active. The exhaust tips are also still clean, and free of build up after driving at highway speeds for over 100 miles. (I clean off dirt n stuff from the car, I cleaned out the tips while I was at it last)

I was also told not to swap the sensors over as that will piss off the computer, so I'm gonna try to check the connections and test the sensor and it's wiring with the engine off. When I got the car, there was a concerning amount of cables not connected all the way, or practically lose. Clips that weren't clipped and hoses that were lose.
As I said, carvana techs don't know what they're doing it seems.

[KillboyPowerhead]

B1S1 (green) should look a lot more like B2S1 (yellow), and both S2's should look more like straight-ish lines. I believe once sensor 2 averages above 700 or 750mV for long enough (or however it works) the P0420/P0430 codes trigger (based on my situation where one of my sensors average ~760mV and the other ~690mV, and only have one code, not both). Also have a V6 but guessing the same sensors are used? Got P0420 soon after installing cams, but never got the code after 3 years with high-flow cats.

Considering both S2's are washing I wonder if the supercharger toasted the cats. High-flow or stock cats?

Edit: was this whole minute at steady state driving? Coasting can make the voltages read low, from fuel cut-off I assume.

[gtstorey]

No problem with replacing the sensors, as long as you use NTK, Denso or GM, but I do know that will fix it. I also don't know that any of your cleanliness test mean much since the cats job isn't to remove carbon.

Stock cats tend to not play well with a supercharger and aftermarket high flow cats struggle to do enough to remove the emmisions.

[Stormo]

Update: Uncle (who is experienced with GM) told me to reseat the sensor cables, and I did. It seemed to have made quite the difference, and gave some insight as to what could be wrong.

Carvana techs



Updated Again: If the O2 sensors are indeed fine, it looks like bank 1 is running rich. Despite not throwing codes, ever. Is this normal?

[Stormo]

Originally Posted by KillboyPowerhead

B1S1 (green) should look a lot more like B2S1 (yellow), and both S2's should look more like straight-ish lines. I believe once sensor 2 averages above 700 or 750mV for long enough (or however it works) the P0420/P0430 codes trigger (based on my situation where one of my sensors average ~760mV and the other ~690mV, and only have one code, not both). Also have a V6 but guessing the same sensors are used? Got P0420 soon after installing cams, but never got the code after 3 years with high-flow cats.

Considering both S2's are washing I wonder if the supercharger toasted the cats. High-flow or stock cats?

Edit: was this whole minute at steady state driving? Coasting can make the voltages read low, from fuel cut-off I assume.

This was while the car was at idle after a drive. I do not know if the previous owner used stock cats or not (We assume he knew what he was doing as everything else that carvana techs did not touch was perfectly fine). I do know that the headers were not used, as the heat shield has a shine to it still, and the gasket on it is new as well. So I cannot tell for certain if the cats were used during the FI state. I am also unsure if it is cammed or not, as I don't know how to tell without tearing down to it.

[Stormo]

Originally Posted by gtstorey

No problem with replacing the sensors, as long as you use NTK, Denso or GM, but I do know that will fix it. I also don't know that any of your cleanliness test mean much since the cats job isn't to remove carbon.

Stock cats tend to not play well with a supercharger and aftermarket high flow cats struggle to do enough to remove the emmisions.

I replied to KillBoy, and I would use the same principal. However I thought of something else to add.

I had the exhaust redone as some of welds were crap (previous owner custom exhaust, bad weld job). I went with meineke. If I knew how to weld and had the space I woulda tried it myself. And knowing meineke, if they saw bad cats when they dropped the exhaust, they likely woulda thrown me under the bus, and tried to tell me my car will spontaneously combust and blow up on the street if I do not buy a cat right now and have them install it.

Is there a more reliable way to determine the condition of the cats without a $1000 emissions tool. I'd assume that smelling for smelly smells doesn't actually mean anything by the replies.

[Stormo]

Originally Posted by KillboyPowerhead

B1S1 (green) should look a lot more like B2S1 (yellow), and both S2's should look more like straight-ish lines. I believe once sensor 2 averages above 700 or 750mV for long enough (or however it works) the P0420/P0430 codes trigger (based on my situation where one of my sensors average ~760mV and the other ~690mV, and only have one code, not both). Also have a V6 but guessing the same sensors are used? Got P0420 soon after installing cams, but never got the code after 3 years with high-flow cats.

Considering both S2's are washing I wonder if the supercharger toasted the cats. High-flow or stock cats?

Edit: was this whole minute at steady state driving? Coasting can make the voltages read low, from fuel cut-off I assume.

Quick research found that the O2 sensors are different between V8 and V6.

[KillboyPowerhead]

There are two cats per side on the stock exhaust, and I imagine if high-flow cats were installed there'd only be one per side.

Looks like bank 2 is fine and bank 1 has a suspect cat; sensor 2 should read like it does on bank 2 - when it reads like sensor 1 (wavy instead of flat) it general means the cat isn't cleaning the exhaust. I believe on the V8 (not sure about the 6 since I didn't do any data logging before installing high-flow cats) the sensor 2 voltage should read around 450mV on stock cats, so since yours is reading higher it may indicate high-flow cats (although there could be other reasons for this too). See post #32 and #34 https://www.camaro5.com/forums/showt...=466464&page=3

Apart from replacing the cat, you can have someone with HP Tuners turn off the P0420 code to make it disappear which is what I ended up doing. As a side note, I noticed if I increased overlap between the cams the sensor 2 voltage would read lower, so this may also be a way of clearing the code without disabling it; I'll find out eventually if/when I turn the code back on... (obviously can't do this with the V8 due to having a single cam).

[Stormo]

Originally Posted by KillboyPowerhead

There are two cats per side on the stock exhaust, and I imagine if high-flow cats were installed there'd only be one per side.

Looks like bank 2 is fine and bank 1 has a suspect cat; sensor 2 should read like it does on bank 2 - when it reads like sensor 1 (wavy instead of flat) it general means the cat isn't cleaning the exhaust. I believe on the V8 (not sure about the 6 since I didn't do any data logging before installing high-flow cats) the sensor 2 voltage should read around 450mV on stock cats, so since yours is reading higher it may indicate high-flow cats (although there could be other reasons for this too). See post #32 and #34 https://www.camaro5.com/forums/showt...=466464&page=3

Apart from replacing the cat, you can have someone with HP Tuners turn off the P0420 code to make it disappear which is what I ended up doing. As a side note, I noticed if I increased overlap between the cams the sensor 2 voltage would read lower, so this may also be a way of clearing the code without disabling it; I'll find out eventually if/when I turn the code back on... (obviously can't do this with the V8 due to having a single cam).

V8 here.
Awesome information, I thank you.
However I do not think there are high flow cats in it, I had it up on a lift, and the cats look about stock. They don't seem to have that discoloration on them like a used cat would, the color seems to be very consistent with the pipes, if not better.

Id assume this means my sensors are fine, and the bank 1 looking rich is normal? never threw codes which is odd, this is one of the reasons I thought it was a sensor issue. However it's leaning towards cats it seems with more troubleshooting. Though I do not want to shell out a ton of money for some cats, nor do I want to have them all re-welded, and spend a ton of more money. I also still do not have an exact plan to how I would like to build this, I'm looking into a corner slayer track attack, though I don't know if I need more power, or more handling components yet. (I was thinking of putting an E85 kit and high flows, though that might be a waste if I decide to run a little boost, yada yada list goes on)

Also, is this a case of an aged cat, and cannot be revived by manually dropping it and cleaning it?
If I were to clear the code, and run it to inspections/emissions, would it likely still clear?

Apologies for what may seem like dumb questions, I'm quite new to the drive way wrench scene.

[KillboyPowerhead]

Not sure why your bank 1 reads different than 2. Looks like 1 goes just as rich (about the same voltage) as 2 but just doesn't go as lean. One of my banks (1 I think) of my V6 runs richer than the other as well as per the long and short term fuel trends, so not sure if that's a GM thing or what.

The P0420 is a permanent code and once set can only be cleared when the ECU sees the right conditions for some amount of time/number of driving cycles. Not sure if disabling via HP Tuners would hide the code from emissions testing stuff or if the code would still be in some memory that the testing stuff can see (guessing the latter is the case). Maybe do some searches on the HP Tuners forum to see if someone knows.

I would try cleaning the cat if it's easy enough to do. The more clear cells for exhaust to pass through the better it'll clean. Maybe a restricted cat could make sensor 1 show less lean if there's more exhaust (and fuel) near the sensor.

[Stormo]

Originally Posted by KillboyPowerhead

Not sure why your bank 1 reads different than 2. Looks like 1 goes just as rich (about the same voltage) as 2 but just doesn't go as lean. One of my banks (1 I think) of my V6 runs richer than the other as well as per the long and short term fuel trends, so not sure if that's a GM thing or what.

The P0420 is a permanent code and once set can only be cleared when the ECU sees the right conditions for some amount of time/number of driving cycles. Not sure if disabling via HP Tuners would hide the code from emissions testing stuff or if the code would still be in some memory that the testing stuff can see (guessing the latter is the case). Maybe do some searches on the HP Tuners forum to see if someone knows.

I would try cleaning the cat if it's easy enough to do. The more clear cells for exhaust to pass through the better it'll clean. Maybe a restricted cat could make sensor 1 show less lean if there's more exhaust (and fuel) near the sensor.

I'll assume that the difference in rich/lean between the banks is normal then, from you and the fact I never got a code from it.

I dont have Jack stands, and I have inspections/emissions in a day. I wanted to get it checked legitimately just incase anything else fails, though I know they'll flag the cats, or just won't check the ECU and assume everything is OK. I'm not sure what the exact procedure is, because I've seen it done different at the couple shops I've seen it done.

I did a quick check around and on ebay, ebay seems to have a couple reproduction cats for less than a $1000 a set. I don't want just the cats, as I don't know how to weld, nor have the tools and don't wanna spend another 300-600 bucks for someone else to weld it. So I was looking for ones that are complete, with pipe n all. I have a feeling these ebay ones work enough, but aren't good for long term (which I'm ok with because my plans for the car are still skewed). I also saw magnaflow made some for close to $6000 which just absolutely boggles my mind.

I guess what I'm asking is, are these reproduction cat sets that are "made in canada" any good? They have some reviews, but you know how legit online reviews are nowadays l.

[gtstorey]

I would consider the ones on Rockauto, but no personal experience with the Walker Cats.

No matter what what you might want to get the tune checked, but adding a supercharger to Cats often fails.