Hesitation on throttle when warm, negative LTFT (datalogs and vids)
 

Howdy,
I'm going to try and be detailed about this to try and make it informative and maybe make it useful to those getting the same symptoms. I know there are a few threads covering similar symptoms but I'll try and detail new ground if I can. Any insights on things I'm missing or overlooking would be appreciated.

Relevant information:
-2013 BRZ, 84000km, MT
-Injen Intake (earlier)/stock intake (now)
-PLM UL headers
-PLM overpipe
-Invidia front pipe
-Invidia N1
-OFT

Bought in January this year, this was the cheapest BRZ/FRS available near me at the time. It was a rebuilt title due to front end collision and came with the modifications listed above. I purchased this as a project and to use primarily as a track car with occasional Sunday driving (my GTI is a bone stock and very comfortable daily driver). I have only started driving/troubleshooting this past month.

The problem:
From the first test drive, there was a hesitation on throttle most noticable from idle. Recently I have also determined that it something that gets worse as the car warms up. When cold, if you rev the engine the response is snappy, as it should be. When the car is warm it takes a second for the revs to pick up at all, even though the throttle body is opening up. The sound is similar to if you were to make a revving sound with your mouth but took a sharp inhale first. It also shows up when shifting, but is not as noticable.

Here are a couple of crappy videos that may not provide any insight.

Response from idle when cold
https://www.youtube.com/watch?v=UbPkCqO_4WA

Response from idle when warm
https://www.youtube.com/watch?v=4ZI3NHSep5w


I started looking into this problem and found the following resources on this forum (no shortage of good information here!):

High negative STFT and LTFT
https://www.ft86club.com/forums/showthread.php?t=127265

High Negative LTFT on N/A BRZ causing idling issues
https://www.ft86club.com/forums/showthread.php?t=106123

High negative LTFT OFT Stg1 tune
https://www.ft86club.com/forums/showthread.php?t=129889

Throttle Delay Fix.
https://www.ft86club.com/forums/showthread.php?t=115282

MAF Scaling - Open/Closed Loop Fueling info
https://www.ft86club.com/forums/showthread.php?t=64790

OFT - Guide To Dialling In Your OTS Base Tune
https://www.ft86club.com/forums/showthread.php?t=94822


Diagnosis:
After having done some reading I flashed the car with Stg-2-Plus-v4.03 OFT tune and proceeded to drive 3-400km. I started taking data logs to see if I could identify anything that stood out from a "healthy" data log (from Wayno's guide above). A full throttle pull showed nothing seriously wrong but at idle or coasting off throttle the LTFT would sit around -25%. By my observation it seems like in low load or low rpm situations, there isn't proper combustion due to either insufficient spark, unatomized fuel mixture or sensors (MAF/O2) giving improper readings to the ECU.

Early log:
https://datazap.me/u/grant-runion/lo...zoom=2132-3518

Steps taken so far:
-Clean MAF
-Rescale MAF (100km driven on rescale flash)
-Return to a stock air intake (back on standard MAF scaled v4.03 tune)
-Replaced all 4 coils from a part out
-Injector cleaner (0km since putting it in)

Areas I can think of to try next:
-Clean throttle body
-Spark plugs (only checked one so far, looked fine)
-Clean injectors
-Try new MAF
-Try new O2 sensor (front I believe?)

Latest log:
https://datazap.me/u/grant-runion/40...d?log=0&data=1

Again, any insights or new direction is appreciated.

LTFT are ugly at idle, can you provide a copy of your bin file? maybe its corrupt, maf scaling could be off

Thanks for the reply. Link to .bin below

https://drive.google.com/file/d/1Z31...ew?usp=sharing

The tables look good, I don't see anything out of the ordinary. It could possibly be an intake leak, recheck all the intake piping, pcv, sound tube generator, the ltft spike while at idle, if anything try swapping the 02 sensor first.

Thanks for the double check. The O2 sensor might make sense, as when the car is warming up I believe it is running in open loop, therefore not relying on feedback from the O2, which could be incorrect. I'll try that avenue and follow up with results.

YOu know in romraider the table MAF compensation (IAT) ?
that 's shitty from the factory
I saw the best approch of it in Wayne's tune

Stock vs modified:

https://imagizer.imageshack.com/v2/3...922/EAKuCm.jpg

https://imagizer.imageshack.com/v2/3...922/eBc0KG.jpg

Try this, then re scale the maf again and fix the open loop fueling , this table is powerfull and will mess with your existing fueling

Haven't heard of this adjustment before but I may give it a go after ruling out the O2 (new sensor coming tomorrow).
So if I understand, update the IAT table with the values above, datalog, then rescale the MAF. When you say "fix the open loop fueling", do you mean adjust the open loop fueling tables?

I just mean that, if you rescaled the maf already, you ll have to rescale it fully because it will modify the fueling
So yes, try to mod it and rescale from scatch

I have been sitting at -15% on my LTFT at idle, too. This is the richest it has been. Not issues mechanically. My local shop is retuning it next week, so hopefully that fixes it (current tune is Delicious e-tune)

In for any responses!

Gotcha, thanks for the clarification.

So I installed the new O2 sensor yesterday and took it for a short drive. Regrettably it wasn't a magic bullet and the problem remains the same. Not that it is helpful, here is a new data log, the only difference is more time on the tune and the O2 sensor replacement. Next up I am going to revisit MAF scaling, this time with the stock air intake, as last time I was still trying to get the Injen intake to work. Failing that I will try the IAT remapping.

https://datazap.me/u/grant-runion/20...g=0&data=1-2-9

Now you can try the IAT mod, here is a modified bin for you to tryhttps://1drv.ms/u/s!Ag-eZ5hz5VnEy3q1...Y6Vrl?e=0yQa2W

I checked out that .bin but it looks like it is the same one as I had on my tune already. Regardless, I did manually put in the values as shown in tomm.brz's post and flashed again. I have only had one drive on the tune so haven't been able to log for MAF rescaling, so that is up next. No noticeable change with the IAT rescale but I hadn't expected that right off the bat.

As a side note, previous to the IAT rescale, I did logs on Friday morning and afternoon on my way to and from work and it was interesting to see the difference that air intake temperature has on LTFT. In the warmer temps in the afternoon the LTFT was only around -11 at idle/off throttle and even in the positives at normal speeds. I don't know if there is anything to glean from this, but I didn't expect it when I looked at it.

Friday Morning
https://datazap.me/u/grant-runion/21...g=0&data=1-5-9
https://datazap.me/u/grant-runion/21...g=0&data=1-5-9

Friday Afternoon
https://datazap.me/u/grant-runion/21...g=0&data=1-5-9
https://datazap.me/u/grant-runion/21...g=0&data=1-5-9

Been a while since I have been able to work on the car but finally have some kms on the tune. I flashed with the MAF sensor rescale and put on about 140km. The hesitation is still there regrettably. I'm trying to gleen something from the datalog but I'm at a loss as to what to make of it. Specifically, at idle it looks like the LTFT is starts high negative then slowly comes closer to 0, while the STFT bounces like a yo-yo. The STFT creeps up, then falls back to a low value, creeps up, falls back to a low value. Is this normal? Any suggestions on where to go next?

https://datazap.me/u/grant-runion/2-...8-9&zoom=0-585

My LTFT/STFT bounced around for thousands of miles until I had enough of it. I switched to CSG and Zach stabilized it throughout the RPM band. He fixed a lot of other issues I had with the car too. I had a problem that my RPM dropped really low for a split second the moment I gave the car some gas and Zach took care of it as well without me having to ask.

I say get a second opinion. It may not be hardware related but software related as long as you're sure that you have no intake leaks or a bad o2 sensor.

Small revelations! But first...

Not sure who this Zach guy is but it sounds like the kind of person that really should be looking at this for me. Part of me wants to keep tinkering but the first Ontario Time Attack of the season is coming up and I may have to tap out and take it to a professional.

With that said, I did have a small revelation tonight. Just because, I unplugged the MAF to either eliminate it or focus in on it. Low and behold, the hesitation disappeared when the ECU was no longer using readings from the MAF. The car even seemed to idle more consitently. This is great, because I can stop asking myself if it is injectors, or vacuum leak, or any other parts I can think to throw money at. Unless I am misunderstanding something, I can think of only three possible causes now:

1. MAF scaling is still not correct and needs to be done again
2. MAF sensor is bad or damaged
3. Wiring harness to the MAF sensor is bad or damaged

I'm not sure why I had not thought to do that earlier, but super glad I did. Hopefully next post will be a resolution of some sort.

Just as a side note, Zach is a well renowned tuner for this platform and works for CSG (CounterSpace Garage).

TENATIVELY SOLVED
I tried one more MAF scaling with 6 good datalogs to make sure the data was clean and it was still no good, even got as bad stalling out at stop lights. I bit the bullet and bought a new MAF sensor, installed it and reflashed with the off the shelf Stage 2+ tune. Right off the bat the the throttle response was great, idle was steady and it shifted much smoother. I only have about 30kms on it but my confidence is pretty high that this is resolved now. So, the takeaway:

If you are having issues with bogging at low load situations and have sketchy LTFT readings, try disconnecting the MAF and see if the problem goes away in the absence of MAF readings. If that is the case and scaling gets you nowhere, you may have a bad MAF sensor.

Thanks to everybody who chimed in with advice, much appreciated!!!