Negative LTFT???

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So I have playing around with my BlueDriver, and the truck's been running good lately. I noticed that the LTFT % is in the negative for both banks. (at idle) They are still roughly the same if I drive 3 miles to the office and still around the same after a long hour country road drive. According to a ScannerDanner video, he says anything +/- 5% is nothing to trip on, but these are a bit past. So it seams like the CPU is cutting back on fuel. Any ideas? Normal? Pressure regulator? TIA.
 
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Keep driving it for awhile. If it stays at -7% or moves closer to zero, don't worry about it. If you start closing in on -10% then I'd do something about it.
 
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Try cleaning the MAF sensor and running a bottle of techron in the fuel. I wouldn't worry too much about at this point. You can check the fuel pressure, if the regulator has a hose pull it off and see if any fuel is present if there is its gone. Check the pressure with the hose on and off you should see a rise with the hose off. Check the vacuum hose for leaks.
 
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Nothing to worry about. Pay attention to SFT and LFT and notice under what conditions the SFTs change rapidly, or if they change rapidly. If it gets worse: MAF concerns and fuel pressure (too high at idle) can mirror each other, rich idle trending leaner under load). Might be a good idea to take a look at the MAF hotwire and see if it has a case of the "fuzzies". Don't know if that year has an actual regulator or a returnless fuel system. Either hook up a fuel pressure gauge, or see if there is a fuel pressure PID available in your scanner software. Relax.
 
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1) Check the air cleaner for restriction. 2) Check fuel pressure regulator or any vacuum hose connected to the regulator for leakage. These are the the only two things which will make LTFT go negative. When MAF goes bad, it will usually read less and not more. BUT, I have had -7% LTFT on my Maxima for a decade without any ill effect or tripping any codes. So there is really not much to worry about at this stage. If the MAF starts getting old, your LTFT would start becoming less negative!
 
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Originally Posted By: Vikas
These are the the only two things which will make LTFT go negative. When MAF goes bad, it will usually read less and not more.
Kinda sorta....but not quite. Bad/contaminated MAFs commonly trend rich at idle, and lean out as engine load/RPM increase. Part of the diag puzzle is that a bad/leaky fuel pressure regulator can sometimes mimic the symptoms (fuel trims) of a bad MAF. In dealing with Fords, it runs about 98% MAF as the problem child.....but that 2% can be ruled out with a fuel pressure gauge.
 
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Dirty MAF sensors gives you system lean errors; NOT rich condition. Most MAF sensor either have electric wire or thin film resistor but the principle is still the same. The electronics inside the MAF maintains the temperature of the wire/film and determines how much current it is pumping through it. When MAF gets dirty and is coated with dust, it is getting insulated from the incoming air. Therefore less current is needed than when the MAF was new. This results in ECM thinking less air is flowing than the actual. So the amount of fuel injected is less than needed for stoich. To make up for it, the fuel trim has to go in to positive.
 
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So what happens if you have a bad pressure regulator or an injector problem and a dirty MAF? Explain this..
Quote:
Running too rich – High negative fuel trim corrections can be caused by MAF sensor problems, high fuel pressure, leaking fuel pressure regulator diaphragm, faulty evaporative emissions components, leaking injectors, defective O2 sensors, exhaust leaks/pinholes before the O2 sensor, coolant temp sensor problems, and base engine issues such as low compression and incorrect camshaft timing. Running too lean – High positive fuel corrections can be traced to MAF and O2 sensor faults, vacuum leaks from intake gaskets/hoses, unmetered air (intake snorkel leak), clogged or dirty fuel injectors, fuel delivery issues, and exhaust restrictions such as a clogged catalytic converter.
I ruled out pin holes because it effects both banks and Evap issues which would trip a CEL.
 
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Originally Posted By: Vikas
Dirty MAF sensors gives you system lean errors; NOT rich condition.
Just giving you the benefit of 11 years in a FoMoCo shop as a performance/electrical tech. Dirty/contaminated MAFs often read rich at idle, and trend lean, often to the point of bogging an engine when RPM/engine load is increased. To be fair, lean trims show up first. More than once I have dealt with both lean and rich codes on the same vehicle. Once I see lean and rich codes at the same time, I zoom in on the MAF.
 
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That makes perfect sense as I have observed this myself when even after second aftermarket MAF was installed in the vehcile. Finally I asked him to get the OEM MAF and no more wild swings on LTFT. Now after your explanation, it makes perfect sense. If you see both lean and rich codes on same vehicle, do you still try to clean MAF and see if the situation fixes or you always had to replace the MAF to fix it?
 
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Originally Posted By: Vikas
If you see both lean and rich codes on same vehicle, do you still try to clean MAF and see if the situation fixes or you always had to replace the MAF to fix it?
I will always throw a $7 can of MAF cleaner at it first. Sometimes it works.
 

1kickbuttranger

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First off, thanks for all replies!!
Originally Posted By: Trav
Try cleaning the MAF sensor and running a bottle of techron in the fuel. I wouldn't worry too much about at this point. You can check the fuel pressure, if the regulator has a hose pull it off and see if any fuel is present if there is its gone. Check the pressure with the hose on and off you should see a rise with the hose off. Check the vacuum hose for leaks.
MAF is clean, I recently cleaned it and it was clean before as well. Techron gets run every once in a while (last bottle was 8K miles ago)
Originally Posted By: punisher
Nothing to worry about. Pay attention to SFT and LFT and notice under what conditions the SFTs change rapidly, or if they change rapidly. If it gets worse: MAF concerns and fuel pressure (too high at idle) can mirror each other, rich idle trending leaner under load). Might be a good idea to take a look at the MAF hotwire and see if it has a case of the "fuzzies". Don't know if that year has an actual regulator or a returnless fuel system. Either hook up a fuel pressure gauge, or see if there is a fuel pressure PID available in your scanner software. Relax.
Fuzzies?? - I hope not. I am 99% sure it is returnless, yet there is a gizmo on the fuel rail with a vacuum tube going to it- Looking it up it is listed as Fuel Injection Pressure Damper- no idea what it is. The Fuel pump is new OEM if the actual regulator is in that.
Originally Posted By: Vikas
1) Check the air cleaner for restriction. 2) Check fuel pressure regulator or any vacuum hose connected to the regulator for leakage. These are the the only two things which will make LTFT go negative. When MAF goes bad, it will usually read less and not more. BUT, I have had -7% LTFT on my Maxima for a decade without any ill effect or tripping any codes. So there is really not much to worry about at this stage. If the MAF starts getting old, your LTFT would start becoming less negative!
Interesting you mention the Air Filter. I change it yearly and it is just shy of a year. I always use a MC Air filter, and I would normally get the FA1658, and this last time, they gave me the new part number FA1744. There are some differences between the two, and I haven't exactly been thrilled with this filter. I am pretty sure the trims go to zero as I drive, but I'll look. It just seems to be at idle.
 
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Once again unless you have drive-ability issues, there is not much point on keeping eye on the LTFT numbers. If you get a code or the engine is behaving poorly, you will need to dig deeper. You can trust the computer to let you know if it is unhappy with the LTFT numbers :-) Seriously, this is the case of getting a new toy and not really being familiar with it. I am betting this is the first time you have hooked up the scanner which gives you this data. If you want to worry, go to Mode6 Results and then you will have good reason to worry :-) [DON'T]
 

1kickbuttranger

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Originally Posted By: Vikas
Once again unless you have drive-ability issues, there is not much point on keeping eye on the LTFT numbers. If you get a code or the engine is behaving poorly, you will need to dig deeper. You can trust the computer to let you know if it is unhappy with the LTFT numbers :-) Seriously, this is the case of getting a new toy and not really being familiar with it. I am betting this is the first time you have hooked up the scanner which gives you this data. If you want to worry, go to Mode6 Results and then you will have good reason to worry :-) [DON'T]
Good point. And yes, first time on a live data scanner... So of course when I see slightly odd things, I may overreact. I think I just saw an unusual blip reading from my 02.. need that fixed now wink
 
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If you leave this connected, then watch for timing advance. I could correlate car's perceived peppiness on a day with observing high values of the timing advance. I had UltraGauge hooked up at that time to my daily driving car.
 
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