Well that's a relief. All I've been hearing is "If you get a header, you need a tune or you'll melt your pistons!" lol
Thank you for taking the time to type this stuff out. Google Fu is what I've been doing so far, but as I'm quickly finding out, I don't know what I don't know lol
One last question, if that's alright; I've noticed a huge argument in every forum I look for on the topic of whether or not you can delete the downflow O2 sensors and replace those with the wideband ones on catless headers, while plugging O2 sensor emulators into the original downflow harness. Would you recommend doing it this way, or would you drill a new hole for the wideband sensors?

 

No worries man, we're on here to help each other out

Yep what you are saying will work. Having no cat upstream of the wideband sensor is the important part though, otherwise it will mess up the readings. The sensor being placed a bit more downstream than what was intended from factory (compared to the original upstream narrowband) will be a bit detrimental to response times and accuracy, but I don't think it will be significant.

Drilling and welding a new hole for the wideband is the best option though, but not always an option depending on the skills available to you.

Another option I have ran on my own car for a while is that I just replaced the primary upstream o2 sensor with the wideband sensor. For this to work you need a wideband sensor/controller with integrated simulated narrowband output. You then use that output to replace the original narrowband o2 sensor signal and feed the stock ECU.
However after a while I was having some issues with my wideband I never managed to fully resolve (mostly due to lack of interest in fixing it) where it sometimes lagged out for a while and then recovered again. But since it was feeding the ECU with this data the engine would stall out when that happened.
No bueno but getting an aftermarket header was in my plans anyways so I got one with dual o2 sensor holes and was able to keep both the narrowband (for ECU signal) and wideband (for monitoring) pre-cat.
I personally don't like running fully catless because of the smell and I am too lazy to swap one back in for the yearly governmental inspection emission tests.

 

Hi all,

I read thoroughly throughout the thread. However, I see no conclusions to the DanielleAlek's running lean problem. I just bought headers because one of my cat gone bad, and Lexus quoted me EUR 4000.... I don't want to damage the engine by just slamming a header in and wait for the consequences.. Can someone advice on what to do to safely run the headers without as said frying the piston rings ? At the moment I am quite limited on economics so I am looking for a rather cheap option. from what I understand, Apexi AFC doesn't work without a wideband and I don't understand if it would work with the stock ECU.

Thanks a lot and cheers,
Eren

 

A header swap is not going to lean out the engine to a level where it causes any damage, you'll be fine

 

What Scigheras said is kinda my takeaway from this thread, so I'm mostly summarizing them and supplementing it with my own knowledge and experienced I've gained in the past year.
8-12% lean is within the "safe" margins. As a mechanic, I'd generally say "That's a bit odd" when seeing those sorts of fuel trims on a stock engine, but I wouldn't raise alarm bells about it unless there were other symptoms.
If you're in a situation where you'd be putting your engine at risk because of headers, you're prolly in a situation where you should be getting a tune, anyways, y'know what I mean? If you're not constantly slamming WOT and redlining the car, you're very unlikely to see any issues. These margins are within how far out of spec older engines can get just all on their own for a variety of reasons, and the ECU is compensating enough on its own to not worry too much.
Apexi AFC doesn't work without a wideband, correct, and neither will basically any tuner.
It works with the stock ECU by piggybacking off of it; it receives the signal from the sensor, then sends its own version of the signal to the ECU to "trick" the ECU into changing the air/fuel ratio (ex. tell it the car's running 15% lean to get more fuel).
If you really think about this, it's basically just giving the ECU a signal to get it to increase or decrease the amount of fuel it's putting into the cylinders. Is that not what the ECU is doing all on its own already? If you're looking for stock performance, the ECU will prevent your engine from destroying itself, all on its own, with the original O2 sensors, just by reading the signal and correcting.
If your only change is headers, a tune is just going to be a more optimized, performance-oriented version of what the ECU is already doing.
I think there's been no "conclusion" because tuning is super complicated, and the conclusion kinda was just "It's good enough as it is" lol
Get a scantool and watch your fuel trims for a while. If it goes above like 20%, then you can start worrying. If it stays below that, just run it as-is.