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elevatef STFT when coasting at idle in neutral

ManBearPig

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I have been working with Lund to try to dial in the MAF curve on my JLT intake. I have started paying close attention to the fuel trims on the nGauge as I drive and I have noticed a trend.

If I toss the car into neutral and let it idle down while I coast down the road, the STFT shoot to about +20% and stay there until I come to a stop, then they settle down. If I am close to a stop before putting the car into neutral and stopping, the short term trims only get out of line for a few seconds before calming down.

I once wanted to see if the trims would eventually settle down while coasting and even after coasting half a mile or more they stayed elevated. Even to the point that the LTFT started climbing....they got up to 13% before I came to a stop. Once at idle, the short trims slowly pulled the long trims back down close to zero.

The trims are pretty close everywhere else. Within 5% at least.

Is it possible that the short trims stay elevated when I’m moving because there is air being forced into the airbox and the pcm has to add fuel to compensate to keep it at 1.0 lambda?

Just a theory, but it makes sense to me.

Thoughts?
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ChiTownStang26

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@ManBearPig

Couldn't tell you why but agree with you on your hypothesis. I can tell you I see the exact same fluctuations since stft and knock sensor are something I stare at while driving more than the road.
 

Tommy V

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While coasting its normal.for stft to max out at 20 until u get close to stopping.
 
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ManBearPig

ManBearPig

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Not sure if I juts never payed attention on the stock intake or ifnit didn’t do this.

Just to clarify, I’m not talking about DFCO going to 2.0 lambda while engine braking. I’m specifically referring to rolling idle in neutral.

I asked Lund, hopefully they can give me a logical answer that convinces me it’s to be expected and nothing to worry about.
 

Bluemustang

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This is why I'm glad I dont have my log data displayed every time I'm driving, otherwise I would worry about every little thing.
 

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ManBearPig

ManBearPig

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This is why I'm glad I dont have my log data displayed every time I'm driving, otherwise I would worry about every little thing.
Lol, yeah. I wish I didn’t even know to watch this stuff. I should probably remove my nGauge from my vent. Would definitely make for a more relaxed driving experience.
 
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ManBearPig

ManBearPig

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Lol, yeah. I wish I didn’t even know to watch this stuff. I should probably remove my nGauge from my vent. Would definitely make for a more relaxed driving experience.

As a side note...I’m wondering if I should’ve gone with a Steeda intake since the MAF housing seems to be more precision oriented with its CNC aluminum tube vs the JLT’s plastic that isn’t the smoothest inside....
 

Bluemustang

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As a side note...I’m wondering if I should’ve gone with a Steeda intake since the MAF housing seems to be more precision oriented with its CNC aluminum tube vs the JLT’s plastic that isn’t the smoothest inside....
Tons of people running JLT with no issues. I've been running mine with Lund tune for at least a year with no issues. Sounds like the OCD might be getting the best of you. Happens to many of us! Lol
 

Zelek

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Just drive your car man. Lund knows what they are doing. Unless you're on the side of the road with a CEL, you're fine. If they've confirmed everything looks good after logging, drive and enjoy!
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