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Your wheel alignment has an allowable range. Do you want yours aligned at the very edge of that range, or do you want it dead center?
There is a big difference between wheel alignment and fuel trim. The ECM is keeping the engine on the fine edge of tune, that is it is keeping it a a 14.7/1 air/fuel ratio. But go ahead and drive yourself crazy (and broke) trying to keep the fuel trim at 0% all the time.
 

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There is a big difference between wheel alignment and fuel trim. The ECM is keeping the engine on the fine edge of tune, that is it is keeping it a a 14.7/1 air/fuel ratio. But go ahead and drive yourself crazy (and broke) trying to keep the fuel trim at 0% all the time.
Your confused, 14.7 is air pressure @ sealevel, An ICE won't run at that ratio, a normal A/F ratio will be 12/1 +-1
 

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2016 Frontier SV 2WD
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Discussion Starter · #24 ·
I have a 2016 Sonata and a Tucson, both with around 50K miles and LTFT is 0 on both vehicles. If someone has a Frontier around 50K miles and a OBD2 reader, could you please post the LTFT of your truck?

My understanding is that if the fuel system is working as expected LTFT should be close to 0.
 

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I have a 2016 Sonata and a Tucson, both with around 50K miles and LTFT is 0 on both vehicles. If someone has a Frontier around 50K miles and a OBD2 reader, could you please post the LTFT of your truck?

My understanding is that if the fuel system is working as expected LTFT should be close to 0.
Did you run that Berrymans injector cleaner through yet?
 

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2021 Frontier SV CC 4x4; 2018 Frontier SV KC 4x2
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I have a 2016 Sonata and a Tucson, both with around 50K miles and LTFT is 0 on both vehicles. If someone has a Frontier around 50K miles and a OBD2 reader, could you please post the LTFT of your truck?

My understanding is that if the fuel system is working as expected LTFT should be close to 0.
I have a Frontier w/ ~70K & an OBD2 scan tool. But my truck runs just like the day I brought her home, so I’ll just let the computer do it’s job & not go lookin for trouble where there ain’t none.
 

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Your LTFT can vary with every tank of gas you buy and especially when the oil companies switch between winter and summer formulas. The reason is that while 14.7:1 is the ideal A/F for pure gasoline, todays gas has additives, most notably ethanol. Ethanol has a stoichiometric A/F ratio of 9:1. The stoichiometric A/F of a 10% blend is about 14.1:1 and that is what the programmed values are based on.

However, the 10% blend can vary. It can't go lower (by law) but it can go higher. A lot of gas is closer to 15%, but it does vary so your LTFT will vary as well. And this is only one factor of many factors that are benign that can cause it to vary.

Someone compared this to a front end alignment. Now I am pretty OCD with my alignments and I do my own with jigs and actual measuring tools. I don't trust computer alignments because they have to be kept calibrated and so often they are not properly calibrated.

But for example you have aligned your front end perfectly, no edge of the tolerance for you. It is dead center of the spec. Now let's just look at toe for example. If the truck is perfect and the alignment is dead on, but you get this crazy idea that if everything is just right, then the thread count on the outer tie rods from the start of the thread to where is disappears into the jam nut should be the same on both sides.

So you crawl down there and count the threads on each side and Oh Darn (or words to that effect), one tie rod has 32 threads showing and the other has 35. Now that could be because the steering box is off because the bolts that hold it are against one side of the hole, or a control arm bushing isn't perfectly centered or slightly worn but still on tolerance. A ball joint may be at the edge of its tolerance, the frame could be slightly bent.

Just exactly how much money do you want to spend just to get the thread count to be the same? If the thread count was off by a lot, say 20 on one side and 45 on the other, then something is clearly wrong and a thorough inspection needs to be done and repairs made. But for a difference of two? Don't worry about it.

It is the same for LTFT. It varies a little from the pre program values but that is OK. The engine management system is keeping the engine perfectly aligned but had to make some adjustments from the "ideal" or expected values. That is what it is supposed to do. If it gets too far off, then you get the DTC and check engine light telling you that something is not working according to plan. Something is out of spec. That is when you worry about it.
 

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Discussion Starter · #31 ·
Your LTFT can vary with every tank of gas you buy and especially when the oil companies switch between winter and summer formulas. The reason is that while 14.7:1 is the ideal A/F for pure gasoline, todays gas has additives, most notably ethanol. Ethanol has a stoichiometric A/F ratio of 9:1. The stoichiometric A/F of a 10% blend is about 14.1:1 and that is what the programmed values are based on.

However, the 10% blend can vary. It can't go lower (by law) but it can go higher. A lot of gas is closer to 15%, but it does vary so your LTFT will vary as well. And this is only one factor of many factors that are benign that can cause it to vary.

Someone compared this to a front end alignment. Now I am pretty OCD with my alignments and I do my own with jigs and actual measuring tools. I don't trust computer alignments because they have to be kept calibrated and so often they are not properly calibrated.

But for example you have aligned your front end perfectly, no edge of the tolerance for you. It is dead center of the spec. Now let's just look at toe for example. If the truck is perfect and the alignment is dead on, but you get this crazy idea that if everything is just right, then the thread count on the outer tie rods from the start of the thread to where is disappears into the jam nut should be the same on both sides.

So you crawl down there and count the threads on each side and Oh Darn (or words to that effect), one tie rod has 32 threads showing and the other has 35. Now that could be because the steering box is off because the bolts that hold it are against one side of the hole, or a control arm bushing isn't perfectly centered or slightly worn but still on tolerance. A ball joint may be at the edge of its tolerance, the frame could be slightly bent.

Just exactly how much money do you want to spend just to get the thread count to be the same? If the thread count was off by a lot, say 20 on one side and 45 on the other, then something is clearly wrong and a thorough inspection needs to be done and repairs made. But for a difference of two? Don't worry about it.

It is the same for LTFT. It varies a little from the pre program values but that is OK. The engine management system is keeping the engine perfectly aligned but had to make some adjustments from the "ideal" or expected values. That is what it is supposed to do. If it gets too far off, then you get the DTC and check engine light telling you that something is not working according to plan. Something is out of spec. That is when you worry about it.
Thanks for sharing your insight!
 

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Discussion Starter · #34 ·
Presumably they are using the same fuel source as the Nissan.
I always go to the same gas station for all three vehicles, the only difference is that the Frontier has 130K while the other two around 50k. I think this is a good discussion if someone is curious to know the LTFT numbers of their vehicle.
 

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One more thing that don't think was mentioned is the air filter. As it gets more restricted, you have to open the throttle slight more for the same power so now the TPS signal is causing the ECM to inject less fuel than the imbedded program would expect because it does not know the condition of the air filter.
 

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One more thing that don't think was mentioned is the air filter. As it gets more restricted, you have to open the throttle slight more for the same power so now the TPS signal is causing the ECM to inject less fuel than the imbedded program would expect because it does not know the condition of the air filter.
The MAF also measures absolute pressure of the incoming air. This accounts for the increase pressure drop across the air filter as the contaminants accumulate. I think the variation in atmospheric pressure day by day is larger than any change due to the air filter.
 

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The MAF also measures absolute pressure of the incoming air. This accounts for the increase pressure drop across the air filter as the contaminants accumulate. I think the variation in atmospheric pressure day by day is larger than any change due to the air filter.
Yes, the MAF measures volume, density, and in many cases including Frontier, temp of the incoming air. Anything prior to the MAF is irrelevant.

Based on that and other sensors, the ECM fires the right amount of fuel. If the O2 in the exhaust is not correct for that amount of fuel, the next firing is trimmed up or down until it is correct. Anything going wrong between the MAF and the O2 sensor will screw things up - vacuum leaks, dirty injectors, defective spark, compression, exhaust manifold leak. The long term fuel trim should be at or very near zero if all is good. When there is a problem, the fuel trim grows +/- to compensate for the problem, and eventually sets the malfunction light.
As confirmed in this thread, many folks are content to live with it, as long as the light is off.
 

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I think the variation in atmospheric pressure day by day is larger than any change due to the air filter.
Yeah, I don't know what made me think of that. I knew that right after I posted it and was going to delete it, but we lost power. Must of been something big as it was a wide area power outage and we didn't get it back until about 8:30 this morning. My bad.
 
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