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It doesn't take but a portion of this video to see what I'm talking about.

My rear o2 sensor voltage seems to run at a steady rate sometimes, then others one or both of them will start to oscillate around wildly, much like the video you posted for me Noodles.


I have a couple of logs to review in graph format, I just haven't yet. The laptop and the tablet I have to use are getting old, and a real PITA to use. They freeze up and all kinds of mess and it always takes 3 times as long as it should to do anything on them.

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The rear O2 sensors are moving around too much. Also, if your cat temp data is in *F, they are def not doing their job... way too cold.
 

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Discussion Starter #22
The rear O2 sensors are moving around too much. Also, if your cat temp data is in *F, they are def not doing their job... way too cold.
Well, I don't know what to say about that cat temp. I have two config files on my device right now. One is the file I used to log with @Boostking . It only has cat temp bank 1, but it's the exact same PID, exact wording. That config file reads 2-300 degrees hotter consistently. I've flip flopped back and forth immediately a few times to verify, both driving and idling. Both config files were built in this truck with parameters validated.

I don't know which set of data to believe on that, and can't explain why they read cooler on this particular config file. The other file shows 1200-1400 degrees driving around town, but again in only shows the temp on one bank, and I don't have rear o2s configured into that one at all.

I REALLY am not looking forward to removing the downpipes and installing new. I'm excited about the possibility of an upgrade, but to be honest that's not a job I really wanted to do. I had decided the benefits weren't worth the rewards before this. I thank you very much.

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Discussion Starter #24
I do. I don't know that I can be absolutely certain though. I think that's what the oscillation on the rear o2 voltage is telling us, but I'm learning as I go here. I'm still going to swap in the spare front o2 sensors. I really don't have anything to lose there, and I don't think the truck is in any danger as of now. As in I think it will be fine to run a bit longer. It runs and idles fine, power is fine, no smoke, cats don't rattle when struck with a mallet, etc.

I do wonder if I should fear some other problem that CAUSED the cats to go though. But, at 80k, maybe it's just one of those things. I think it's not too uncommon for our turbos to puke a little oil which would help burn out the cats over time. Maybe?

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Cats are more fragile that most folks think. A little bit of oil or raw fuel when they are hot, can cause issues. you may be able to find a set of take-offs if you wanted to stay stock.

I can't say for certain, but based on your data, I would say you have under-performing cats. The fact that you still get the codes "stock", usually means something is up. The rear O2's are way cheaper than the fronts (for my truck at least) and you'll want to put in new ones anyway, if you're gonna swap DP's.

Just a FYI, but here is what the cats looked like on my 2000 F150 (5.4 Pro-charged) after I had a injector stick open...

 

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Discussion Starter #26 (Edited)
I'm absolutely not staying stock if I go through the trouble of pulling the downpipes, I just didn't want to have to pull them in the first place. If I do, I think I'm going catless. I'm not going to take a chance on having to do this every 80k miles.

The rear o2 sensors are about 24 dollars each from Tasca. I'll have to use the O2 extenders. If I do that is there any reason to get new rear o2 sensors? The fronts run about $90 for the pair, which is why I want to try my spares first.

I figured out the cat temps. I never thought to check the units @noodles (I didn't set the units specifically on the other file either). It was indeed in Celsius. Reading 1200 ish cruising this morning.

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If the front sensors are reading off, it will mess with your actual AFR and your rear o2's will pick it up.

I wouldn't change the rears, if you end up going catless. Just throw in the extenders and see how it goes.
 

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Discussion Starter #29
Did any of you swap downpipes without hacking up the original?

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Discussion Starter #30
I finally got around to changing my o2 sensors today with the old ones. I don't know what I was putting it off for, took all of about 10 minutes to change both of them.

No change in anything. Although I don't have a CEL back yet, the data shows the same thing. I expected that though. I figured if an O2 sensor was the culprit causing the data I've seen, it would be downstream. I still haven't ordered any for downstream. I may just order one and see what it does on that particular bank. No need in wasting $25 x 2.

On another note, SPD catless downpipes are like $380 shipped right now...

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