Newbie Looking at O2 sensor data

[pkufeldt]

Pretty sure I have wrecked my cat but I thought I would post something and see if anyone could help confirm. Just finally fixed a long standing misfire stemming from a worn distributor. As part of diagnosing the misfire, before I figured out it was the distributor, I replaced the stock SFI injector with an MFI injector and evidently shredded the injector upper intake o-ring. This of course left me with a pretty severe intake leak, leading to LTFTs in the mid 20s. So I was running real lean while misfiring like crazy. Well both are now fixed, intake smoke tested - no leaks - and new distributor got me to CAM retard of 0 with no misfires. But now I have popped a P0430 and my downstream bank2 O2 sensor looks to me like I fried my cat during this process. Attached is my latest data, it still shows higher than acceptable LTFTs (10-15), but I am assuming its because of O2 sensors data. So my question is based on this data is the answer most likely the cat or could there still be bad O2 sensors. These charts are from the same 800 second test drive sequence.

BTW it is a 1999 5.7L K1500 Suburban.

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[Schurkey]

Pretty sure I have wrecked my cat

"Cat" singular? Don't you have two? Looks like one works, one doesn't based on the O2 sensor data.

Well both are now fixed, intake smoke tested - no leaks - and new distributor got me to CAM retard of 0 with no misfires.

Did you clear the previous codes and saved computer trims--fuel trims, etc?

Attached is my latest data, it still shows higher than acceptable LTFTs (10-15), but I am assuming its because of O2 sensors data. So my question is based on this data is the answer most likely the cat or could there still be bad O2 sensors.

Downstream O2 sensors don't affect fuel trims. Upstream sensors can.

At first glance, the graphs appear to show lots of cross-counts. But I'm not used to seeing 800 seconds (13+ minutes) worth of cross-counts on one display. The more I think about 800 seconds, and the sensor activity, the more I think the sensors may be lazy. How old (age, mileage) are the O2 sensors?

 

[pkufeldt]

Just disconnected my battery to reset FT, thank you.

About the cats. My bad, I knew there were 2 cats, just wrote it up wrong. Was mostly suspicious about the cat off bank2 cause downstream sensor seems to follow upstream. But cat off bank1 looked different and made me wonder about the sensors. My expectation is that both downstreams should be flat lining. B2S2 was replaced recently (<5k miles) all others are original equipment with 130k miles.

Should I just replace the sensors, get new data to confirm either one or both cats are dead/failing?

BTW I can't weld in new cats so I will be replacing both with a direct fit from AP.

 

[Road Trip]

Greetings pkufeldt,

Welcome to the GMT400 forum! Don't know if you've lurked prior to
posting, but Schurkey is a Subject Matter Expert, and you are in
good hands.

****

Listen, the fact that you are A) already capturing data, and B) are having
issues with your long-suffering cats, you may be in a position to
factually prove/disprove what I've heard from several people that
I trust. (But I haven't had the need to try this 1st-hand?)

What I propose is that you try a catalytic converter cleaner that
several mechanics around here swear by in order to get a car
past the annual NY emissions test. (CEL lit, P0420 code, etc)

After trying said 'fix in a bottle', do your data capture, upload to
here, and then we can compare your original data vs. post 'cat clean'.

If there's no change, then we know. If there is a change, then we
can quantify the improvement & file that away for future reference?

Here's the magic juice that (supposedly) gets your tired ride another
sticker for another year:

You must be registered for see images attach

Here's the Amazon link: (link)

I read through a few of the customer reviews, and in general they sound
similar to what the mechanics told me. Big picture, this bottle won't
repair a bad wiring harness down to an O2 sensor, or unmelt a cat
where the honeycomb has been Chernobyl'd. And a few of the reviews
are wondering if the fact that the power windows quit working shortly
after using the cataclean is the fault of the product? :0)

Seriously, I'm trying to separate the troubleshooting wheat from the chaff,
and you might be a perfect candidate to do just that.

As for whether this actually works on not? In the second review down
a gentleman (possibly with a chemistry background) said that this
product generates Carboxylic Acid, which acts as a solvent to
remove the surface layer of crud & baring the underlying platinum
to the passing exhaust gas, allowing the catalyst function to restart?

****

As I mentioned above, I haven't had a P0420/30 code to work on since
this stuff showed up on the parts store shelves, but if the opportunity
presented itself I would do all the standard revival stuff first, then the
'cat cleaner'. (Fresh plugs, oil change, air filter if needed, Italian tuneup,
go to emissions testing with the warm afterglow still on.) I would add
the 'cat cleaner' between air filter & Italian tuneup?

Again, I initially dismissed this product as the usual 'engine rebuild in a
can' hokum...but I had a few people I trust tell me that it actually
makes a difference -- to the point that they won't spend the customer's
$,$$$ on cat replacements until they try this first?

Bottom line, I'm on the fence about this stuff, but with your data logging,
and assuming that your cats would still pass a visual inspection, then
maybe this stuff can remove enough of the surface contamination
(from the recent misfiring) ...that it will show up in your data logs?
And possibly even clear that P0430?

Or, maybe the cat clean + replacing a lazy upstream O2 sensor will
give the computer what it wants to see?

Whatever happens, best of luck finishing the fix!

 

[Road Trip]

Thinking about this, essentially I'm asking you to spend your money in
order to satisfy my curiosity. (Also hoping that it clears this fault for
you & we can celebrate a big cost avoidance!)

Here's a possible plan B: Go to NAPA & try this product, which 'guarantees'
that you pass or double your money back? I haven't heard anyone around
these parts using this, but it's from CRC, and their solvents generally do
what they claim.

This way you can try this for essentially no money out of pocket. If it was
me, I'd print that out & talk to the NAPA guy at the counter & make sure
that this offer is legit. (And of course if you do all this pls data log & share
the results!

There...I felt a little guilty now. Good luck!

 

[Schurkey]

Just disconnected my battery to reset FT, thank you.

Did that work? I have always cleared codes and trims using a scan tool.

B2S2 was replaced recently (<5k miles) all others are original equipment with 130k miles.

Should I just replace the sensors, get new data to confirm either one or both cats are dead/failing?

BTW I can't weld in new cats so I will be replacing both with a direct fit from AP.

Three O2 sensors that are old enough to vote and buy liquor? They're done. Even if they "work", they'll be lazy--slow to respond. Depending on having to get a "direct fit" catalyst, maybe you put the new sensors in the new pipe, and not have to deal with ripping the old sensors out of the existing holes.

I don't know how tough the 4th sensor was to get out. I seem to have bad luck with O2 sensors about half the time. My Hemi Charger experience was a doozy.

The sensor that's already been replaced is probably good--although to repeat, I'm not used to seeing 13+ minutes of sensor activity on a graph.

I guess it hurts nothing to "clean" the catalyst with magic juice, and then slap in three fresh O2 sensors. I'm thinking that maybe you don't want the magic juice byproducts "cleaning" the new O2 sensors...but perhaps it's harmless. If the juice works...great. I'm kinda guessing that you need at least one replacement catalyst.

 

[Road Trip]

I guess it hurts nothing to "clean" the catalyst with magic juice, and then slap in three fresh O2 sensors. I'm thinking that maybe you don't want the magic juice byproducts "cleaning" the new O2 sensors...but perhaps it's harmless. If the juice works...great. I'm kinda guessing that you need at least one replacement catalyst.

I concur. Since O2 sensors are definitely a wear item, replacing wear items is not
considered loading the parts cannon. And if this truck is a 'keeper' then for
improved driveability, new quicker switching O2 sensors make for a
more responsive feedback loop. The computer is only as good as the
input signals being fed into it. (!)

And I agree w/Schurkey that I would do all my prep work (plugs, oil, etc)
AND experimentation (magic juice) *first* on the old O2 sensors, then swap in the
new sensors & see what further improves via your data log.

And if all of the above fails to revive the polluted cat, only *then* would I spend the
money for a $$$ new one. (Or Cali/NY emissions $$$$ new one. :-(

Kind of a measured response method. You got the engine running right, now
to fix everything downstream for the least out of pocket possible. Good luck!

 

[pkufeldt]

Three O2 sensors that are old enough to vote and buy liquor? They're done.

Too freakin funny.

I am still new enough to this and I haven't invested in a real scanner. I am using a BT Elm reader and an app on my tablet. I am using Car Garage Pro and it doesn't look like I can reset the FT. But disconnecting for an hour seemed to work. LTFT went to 0.4 and sat there for awhile but then as the engine heated up, they both worked their way over 10 again. But lower than before. I am hoping the change in the upstream sensors will help this.

One other thing I noticed about my data is that it takes a significant amount of time to collect data points. In the datasets I have been collecting there is easily 2-3 sec between data points of a particular PID. That is the distance between 2 subsequent Bank 1 LTFT measurements is nearly 3 seconds. I graph them correctly relative to each other but it just seems that is a pretty coarse granularity. Does the ECU do this, collecting a frame of all PIDs at that kind of granularity or this just my bogus App setup?

I have decided on replacing the cats and due to your nudging will retire my O2 old timers. ;-) Thanks again for all your help.