Tuning and LTFT (Long Term Fuel Trims)

BruceH

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It's common during the tuning process. All it takes is turning off adaptive learning. I've left it off before when I had a paxton because of the maf backwash in their standard suck through maf location. The car still ran fine and it didn't learn any bad habits from the poor maf location.
 

michael.konor

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It's common during the tuning process. All it takes is turning off adaptive learning. I've left it off before when I had a paxton because of the maf backwash in their standard suck through maf location. The car still ran fine and it didn't learn any bad habits from the poor maf location.

Should it be done automatically by tuners? You mention that you left it off before, but not always?

Thanks.
 

BruceH

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Should it be done automatically by tuners? You mention that you left it off before, but not always?

Thanks.

It's a good idea to do it while dialing in the maf transfer. I've made corrections with it on too. You just have to add the lt and st together to get the correction. The maf adaptive would still have to be turned off though.

I can only speak for myself. I'm sure that pro tuners do things differently than I do. I have forever to figure something out. Their time is money.

Like I said I left it off with my Paxton when it was suck through. The backwash onto the maf made the trims unstable during transitions. When I had it on the trims "learned" bad habits and would have even wider swings because of the ltft.

You probably already know this but I'll say it anyway just in case. Short term trims are instant feedback from the o2 sensor. Long term corrections are predictions that are learned from short term data. As long as the maf transfer function is good the motor can run perfectly fine with stft only.

Why are you concerned with it?
 

TurboX

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Bruce,
Would you ever consider a thread on tuning ? Im a pretty mechanic hands on type guy but I dont know shit about tuning a modern vehicle. I leave this to the expert(Lito) but I would really enjoy reading about tuning and differences between lets say, NA, SC or Turbo.
 

BruceH

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Bruce,
Would you ever consider a thread on tuning ? Im a pretty mechanic hands on type guy but I dont know shit about tuning a modern vehicle. I leave this to the expert(Lito) but I would really enjoy reading about tuning and differences between lets say, NA, SC or Turbo.

I don't have the skills or experience to be a ring leader. I'm just a hobbyist with software. I do enjoy sharing my experiences or what I do know and helping when possible but that's about it.

I will say that a very good resource is the book "Advanced Engine Management" by Greg Banish. He covers a lot of internal combustion theory.

Eric Brooks has a tuning section on modularfords you could check out if you haven't already.
 

one eyed willy

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Just adding to what Bruce said, adaptive learning needs to be turned off during the tuning of the maf transfer process. It will sku what you are trying to accomplish by making corrections on its own. You dial in the MAF transfer with it turned off so you have actual numbers based on the actual transfer, not something the computer is manipulating. Tune your MAF to around 500 and from there set your open loop chart. Also look at what you have your closed loop/open loop throttle position set to. Make sure it's not too high.

Once you get your MAF transfer dialed in, turn the adaptive learning back on. It will help with drive ability depending on how well the transfer is actually dialed in.
 

Mustangk

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You probably already know this but I'll say it anyway just in case. Short term trims are instant feedback from the o2 sensor. Long term corrections are predictions that are learned from short term data. As long as the maf transfer function is good the motor can run perfectly fine with stft only.

if this is true why does the LTFT seem to add up the STFT, for example: i have stft each bank hovering around 0-2 but once my engine goes closed loop the LTFT climbs up to 20%. indicative of my vacuum leak i think is coming from exhaust bolt hole repair i tapped crooked and leaks oil, a first top manifold hole and i oversized the hole and it broke into valve spring area where theres oil. and leaks at idle.. ???
 

Juice

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I want my LTFT as close to no correction as possible. I use it as an indicator of how good the tune is.
At first reset, both STFT and LTFT are zero until some miles are driven. At first, LTFT will remain zero, and STFT will have a larger swing. Once LTFT matures, the pcm 'learned' the difference between what the engine wants vs what the calibration is set at. At this point, STFT swings will be much less as the pcm is applying the learned (LTFT) corrections.
Turning off adaptive is done to dial in an aftermarket intake where tube diameter at the maf has changed. After that is done, I turn adaptive back on and leave it on.
The more changes, (injectors, maf, cams, stroker, FI) the more difficult the tuning process.
 

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