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Discussion Starter · #1 ·
I'm getting some weird AFR changes and I want to wrap my head around what I should be seeing vs. what I am seeing.

tl;dr: AFR's too lean

For as long as I've had my AFR gauge installed, I've been seeing 13.2 pretty steady whether idle, WOT, off throttle cruise, etc. it didn't really change much.

Went on a short 200 mile trip and on the way back my AFR's started playing around. I was driving and they started slowly creeping up about 1 unit per minute until the gauge maxed out at 18 and just showed ---. Stopped at a gas station, didn't see anything loose or introducing nonmetered air, started the car back up and it stayed steady at 13.2 for the entire 170 mile or so drive back home as usual. The only thing that had changed were elevation and temperature, so I figured it was just a hiccup or a gauge issue.
Started up the car this morning after getting back and my drive this morning had it running like an NA car, with 14.7-15 AFR most of the time, fuel cutting during off throttle cruise lean enough to go off gauge, and only slight blips down to 12 followed by steady at 14.7 on WOT.
Car doesn't seem effected significantly, the exhaust has a slightly different tone to it, but the performance has not been noticeably affected, and I have no CEL or codes popping up.
The tone change makes me think that there is actually a change in AFR's not just a wonky gauge
Boost is unaffected, so that makes me think there isn't a leak.
Exhaust is the newest part, and where the AFR gauge is reading from, so my initial assumption would be a post turbo air leak making the gauge read lean.

Thoughts? Knowledge to drop? Am I making poor assumptions? Places to start diagnostics?
 

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Sounds like a bad gauge/sensor to me. You should be 14.7 at idle and cruise, since you weren't, I suspect the gauge. Also if you were really leaning out into the 18s, the car would've really been running poorly and knocking like crazy if you went into boost like that.
 

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What's your O2's lambda's and delta?
Also to give credit to your theory - you can hop under there and check for carbon buildup around the joints of the exhaust for leaks.
 

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Discussion Starter · #4 ·
I was initially under the impressions that the maps wouldn't shoot for 14.7 on a turbo car, that seems way too lean even for cruise despite it being stoich. But apparently I'm dumb for reasons I'll get to in a second. I'm also thinking gauge is an issue now, but not a bad gauge, just a finicky one.
My O2 has a number of configurations, the one I'm currently on is AFR from a 0-5v source on a linear path. The only lambda option I have is the exact same thing but lambda instead of AFR, then it goes into nonlinear configs but they're all AFR, so essentially my AFR is my lambda. Unless you're asking about the range, then it's AFR 10.0-18.0 and lambda like .75 to 1.25 or whatever that correlation actually happens to be. I don't have data logging, so I don't have any kind of long term trim delta, but the gauge's intrinsic delta is reported as .1AFR repeatably accuracy, and the sensor is 0.7%
Initial inspection of the turbo to downpipe flange doesn't show any carbon buildup, but I haven't had the chance to get under it yet.

After some playing around with getting AFR's to move around, I found that if I'm driving and getting the mid 13's AFR consistently, then stop, turn off the car, turn it back on and then drive, the AFR's appear normal, with stoich on cruise, rich on WOT, and lean on off throttle cruise. This is repeatable. This has me thinking that the sensor needs to be warmed up to get accurate readings, that said, it is a true wideband and that shouldn't be an issue like with a narrowband where rich AFR's are temperature dependent. I'm going to double check the gauge and ensure that the config isn't running on one of the non-linear small voltage options that might be more temperature dependent.
 
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