Originally Posted by Face_Plant (Post 3162854)

My idle has began fluctuating up and down by about 50-100 RPM and the AFR's will swing wildly between 10:1 and 20:1. This only happens when the car is fully warmed up. AC/defroster is off. At cold or semi-warm idle everything is fine. I put the car on my lift while running and I do not hear any exhaust leaks or see any soot that would indicate a leak. The torque for all exhaust fasteners was checked once a week for about 4 weeks after installation to make sure they were still tight. I'm assuming it's an O2 sensor issue since most cars don't use the O2 sensor until fully warm, correct?

Log of 100% warmed up idle:
https://datazap.me/u/jmtrotz/2015-fr...og=0&data=1-13

Log of semi-warm idle, going for a drive, and ending with 100% warmed up idle:
https://datazap.me/u/jmtrotz/2015-fr...og=0&data=1-13

Car details:
2015 FR-S
Shell 93 octane gasoline
Gruppe-S header/over pipe with GrimmSpeed gaskets
Stock front pipe
HKS Legamax catback
OFT Stage 2 UEL 93 v2.076 off the shelf tune
Stock intake/airbox

Originally Posted by MCTeeJ (Post 3162859)

If an o2 sensor is bad it'll usually peg in a direction, either lean or rich. Make sure to check for a vacuum leak up top as well just to cross another item off your list, though not likely with the stock intake. In the mean time, have you tried flashing back to stock to see if AFR keeps swinging like it is? Maybe hit up the resident OFT guy, @steve99.

Originally Posted by steve99 (Post 3162866)

Yes something way off in those logs.


Can you do some more logs but tgis time instead of logging flkc knock correction and intake air temp, can you log port injectpr and direcrit injectoin pulse widths or mght be called injecor open time. I want to see if the injectors are actually injecting in lots of fuel then shutting off.


I suspect its the front 02sensor


The manifold pressure boost is sgowing -8 or so so that indicates no intake leaks


Ltft is low but with afr oscilate​ing like that it provably doesnt mean much.


Check you 02 sensor pligs are tight and fhe di injection computer under bonnet is bolted up tight ( you have not changed the di computer bracket for aftermarket ? )


But the logs of injector pilse widths should help

Originally Posted by tomm.brz (Post 3162982)

Is your ots tune untouched or did you modify it? Have you changed the front scaling in any way around the 0mA value?

Originally Posted by Face_Plant (Post 3163154)

Alright, so I gave the O2 sensors an extra 1/8th turn (they were already pretty tight) and cleaned their connections. The DI computer connections are still good as well. @steve99 here are the injector logs you requested. I logged other fuel related channels just in case.

Cold idle where everything is smooth and the AFR sticks to about 14.5:1
https://datazap.me/u/jmtrotz/cold-id...=0&data=1-8-14

Warm idle where the AFR swings wildly between 11:1 and 20:1
https://datazap.me/u/jmtrotz/warm-id...=0&data=1-3-12

This one is while driving again:
https://datazap.me/u/jmtrotz/drive-home?log=0&data=1

I've noticed that between 2500 and 4000 RPM while accelerating with light/moderate throttle the engine speed will sort of increase in "hops" instead of climbing smoothly. It did it several times while recording my driving log.

I peeked at my OFT while driving and noticed how rapidly it swings between 10:1 and 20:1 is dependant on engine speed. At idle it's a pretty slow flip flop compared to at higher RPMs where it's very rapid. I checked for codes and I have P0171 (too lean) and P219A (AFR imbalance) :(

Originally Posted by steve99 (Post 3163218)

It does look like the front 02 sensor is bad or has some form of wiring issue.


In the idle log you can see the afr go to 20 which is limit of sensor but the injection time is actually increasing, so that seems to indicate o2 sensor issue.


Again while driving you see the afr go super lean but the injection volumes for pirt and di dont drop.


Unfortunatly 02 sensors are not cheap, but it does look like front o2 sensor is bad.


Dont over torque them or drop them they are quite easy to damage.


My try to get one from crashed car, they are all same auto manual alk years i believe

Originally Posted by Face_Plant (Post 3163221)

That's what I was afraid of :( Thank you for your help and looking at my logs!

Originally Posted by jflogerzi (Post 3163296)

You could also try the latest V4 tune

Originally Posted by MCTeeJ (Post 3163330)

Fret not! o2's aren't the cheapest things in the world but they are also not that expensive! I think I paid between 80-100 bucks for mine last year.

Originally Posted by Face_Plant (Post 3163386)

I've tried the v4 tunes. It does the same thing. I flashed the v2 tune to see if was any better. While transferring the O2 sensor to my new header I must've gotten anti seize on the sensor and contaminated it or something. The price seemed to vary between $90 and $200 depending on where I bought it from, brand, etc. Amazon had a Denso sensor for $103, Toyota parts sites wanted about $190, so I went ahead and bought a Denso sensor from Rock Auto for $109 shipped. The sensor itself was $93, one day shipping was only $11, and the remaining $5 was tax.

Originally Posted by MCTeeJ (Post 3163420)

I've got the Denso from RockAuto in my car as well. Works fine.