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Old 04-28-2018, 08:33 PM   #1
86TOYO2k17
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High negative STFT and LTFT

Recently I noticed my car was bogging down and bucking at low throttle, low rpm so I started looking st my fuel trims and at idle, low rpm, low throttle my STFT and LTFT where both around negative 15% (30%), at Highway cruising as well as WOT they are both around 0. I reflashed my tune and car drives better but LTFT is slowly creeping back up as well as STFT being around 15%.

Another issue possibly causing this just never noticed fuel trims from lack of driving and lots of reflashes. I had a shop put on Crawford billet Blocks and a ace 250 header/op. At the time everything else was stock. Besides OFT tune. But only in gear and I only hear it in 1st-3rd gear at exactly 2500rpm and 3000rpm there is a high pitch sort of whistle sound, like a hybrid between a kazoo and a whistle. I went back and had him do a smoke test and he said he didn’t find anything, although idk if I trust him...

From my understanding a high negative fuel trim is from too much fuel. Could this sound have something to do with fuel injector and or fuel rails? Or is it possible exhaust leak at header or OP or vacuum leak at manifold or a loose hose could cause this noise as well as really high negative fuel trims? What should I do?

Last edited by 86TOYO2k17; 04-28-2018 at 08:48 PM.
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Old 04-28-2018, 08:35 PM   #2
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Forgot to add, noise came with just CPB and ace header/op. Although now I am running grimmspeed intake hks double res FP, and CSG mxp catback. On a new 2017 Toyota 86 only 3500miles.
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Old 04-28-2018, 09:31 PM   #3
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Is the car starting harder lately?
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Old 04-28-2018, 09:56 PM   #4
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That car is and has always started just fine. After the initial “warm up” around 1250-1300rpm it drops and stays around 700rpm.
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Old 04-28-2018, 10:31 PM   #5
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Negative fuel trims are from the front O2 sensor reading a lower lamda than it expects.

I would think the trims would be negative across the board in most cases of something being physically wrong. Any other modifications to the car or tune?

The sound you are describing could be gear whine. Or it could be a leak on the intake side.
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Old 04-28-2018, 10:50 PM   #6
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I just have grimmspeed intake, billet power blocks, ace 250 header/op, hks double res FP, CSG mxp catback. With OFT v4.03 tune, on the first revision of my e-tune. But the negative fuel trims don’t appear at WOT or at 65mph cruise. Just idle and low throttle/rpm city driving. And a noticeable difference in performance. With bogging, and bucking. But on hwy and wot car is fine. I haven’t tried flashing any older tunes or back to stock to see, although it can take up to 100miles for it to really “normalize” I did flash to stock and stage 1 to see if driveabilry and noise improved and it did not.
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Old 04-28-2018, 11:31 PM   #7
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You are getting it etuned? Well, check with the tuner to see if they did anything that might cause this. That intake definitely needs the MAF rescaled, so maybe they haven't finished adjusting it. Strange things can happen when the MAF isn't right. Also, might want to clean the MAF, they are very sensitive, particularly at low flow rates.



Also, as I'm thinking about this, it's sounding more like a leak on the intake tract. Lower throttle should have greater vacuum because the throttle plate is restricting flow, but the cylinders still try to fill .5 liters. So a small leak would have a greater effect on low throttle. If there is a leak, it's between the throttle and the cylinders. Could be the bpbs...
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Old 04-28-2018, 11:49 PM   #8
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Yeah shiv is e-tuning. But process is taking forever... maybe the next revision will be better. I always thought one of the “selling points” of grimmspeed intake is it is close to stock maf.
Thought it would be off by maybe +\- 5% not -30%

I’m feeling like something is off with the BPB as well at least causing the noise. But wouldn’t fuel trims be positive if it has more air coming in then it thought?

Going to my step dads tomorrow and putting it on his lift to put on new engine mounts, and few other things. Was hoping to get some ideas of some things it could be Incase it’s a physical issue and I could check tomorrow.
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Old 04-29-2018, 01:03 AM   #9
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Grimspeed intake is close to stock


exhaust leaks usually cause high positive trims at low rpm/idle, that get better as rpm increases




Check you maf install into intake did you put gasket on maf ?? check for intake leaks or creased. damaged maf gasket.


carefully clean maf sensor with maf cleaner it may have oil or dirt on it


watch these videos


[ame="https://www.youtube.com/watch?v=5WnM_NsOtd8"]Secret of Engine Problem Diagnosis- Fuel Trims Pt.1 - YouTube[/ame]




[ame="https://www.youtube.com/watch?v=cARQ0jZZ4Qc"]Secret of Engine Problem Diagnosis- Fuel Trims Pt.2 - YouTube[/ame]






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Old 04-29-2018, 01:51 AM   #10
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Quote:
Originally Posted by 86TOYO2k17 View Post
I’m feeling like something is off with the BPB as well at least causing the noise. But wouldn’t fuel trims be positive if it has more air coming in then it thought?
Oh lol I'm dumb and got everything turned around in my head. I should know better than to try troubleshooting stuff at night .
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Old 08-16-2018, 10:54 AM   #11
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Was this ever resolved? I'm having the same issue with my fuel trims. Extreme bogging and stuttering at low rpm/throttle. Hard to accel, AFR reading max rich 11.02.

Then it suddenly clears up and is fine until it happens again.
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Old 06-29-2019, 03:55 PM   #12
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Anyone figure out the issue? I am having the same symptoms stated above.
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Old 07-11-2019, 10:51 AM   #13
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Can you log your MAP? Had a bad connector on my MAP and it would occasionally go crazy, reading low vacuum so fuel would get dumped in until it hit 11.5:1 and then the ECU would pull the fuel and it would just cycle like that. Car was almost undriveable. And then suddenly it would be fine. I caught it in a log finally and put a new MAP pigtail on to fix it.
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Old 07-11-2019, 02:09 PM   #14
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Could be the gaskets on the power blocks. If they don't seat flat they can leave gaps. Easiest way is to remove them and check to see if they're pinched.
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