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12-17-2008
Just lately I've noticed on my aeroforce that my LTFT's have gone up kind of dramatically (reaching ~14 briefly at times but staying around 5-8 on the highway). What would be the most likely root cause for this? I have a couple guesses but won't list them here for mortal fear of showing my relative ignorance in the fuel trim and tuning arenas.
Hope to maybe be getting a DHP or PT from Santa but even if I do it'll take me a while to learn how to properly use it.
12-17-2008
Could be related to decell enrichment. That is if it is happening when you are de-accelerating or slowing down.May just need a tune. Do you already have one or what? If not 5-8 sounds normal for a stock car that is untuned.
12-17-2008
I'll pose this question, 'cause Im curious and dont completely understand the subject myself, but would cold/winter weather affect LTFT's?
12-17-2008
Yup. Cold air intakes can even cause them. Ideally you should have a different maf .bin or tune for every 20* changes in ambient temp.Long term fuel trims are just an average of short term fuel trims.But both can change with the conditions you mentioned above.
12-17-2008
Yeah, about eight months ago I got a tune from Paul J himself of PRJ after he did 90% of my SSIC install. He's a couple hours away from me but I may have to drive over and get an update but I'm just curious as to what may have changed recently to throw the LTFT's more out of whack. And yeah, they do seem to reach the higher numbers during decell.
12-17-2008
TDC, you and I need to talk about tuning. I have been curious a long time about how to keep a stable tune over such broad temp. swings. I dont want to hijack the thread, but at some point we need to or there needs to be a discussion on the forum about such things.
12-17-2008
Well if that's true that may well be the main cause of my readings going up of late since it's been below freezing around here for the last week or so mostly.Ideally you should have a different maf .bin or tune for every 20* changes in ambient temp.Long term fuel trims are just an average of short term fuel trims.But both can change with the conditions you mentioned above.
12-17-2008
Well, It's easy actually. Say you have a 80 degree day during the summer. All you do is a MAF tune to get you're trims in line. Then you save it and make a note that it is for 80 ambient temps. Or you could simply save the maf table instead of the whole tune.either way it will work the same.
When it gets 10 or 20 degrees colder outside do the same thing. Over time you will have a library of MAF tables for different temps and such.
And thats pretty much it.
Yeah if it's happening on decell then thats what it is.
Last edited by TDCRacing; 12-17-2008 at 12:09 PM.
12-17-2008
I was afraid you would say that is the way to do it, but it makes sense. I guess what I didnt know prior to now was how much of a temp. swing there should before one re-tuned for that temp range.
Its too bad there isnt some way to simulate those temperature variances.
12-17-2008
I belive there is. I'm not firmilar with this product though.Originally Posted by SyntheticShield
It's called an afc. I belive the new one they have out is the afc 2.0. I belive easy performance make it.
It is mainly for timing changes i belive but i belive it works off of the IAT temp sensor and thats how it adds or subtracts timing.The iat table has added and subtracted timing depending on what tempeture it is reading.
Maybe someone will chime in and clear things up for the both of us on this subject.
12-17-2008
Actually I had thought of something like that, but I had concerns with fooling the PCM into thinking its one temperature and its really not. It may add or reduce fueling and/or timing, but without it actually being that temperature I would imagine the combustion process is not going to follow and it could cause some driveability issues. I may be wrong on that, as I mentioned Im no expert in this area, but it would seem to me that if every system and sensor on the car wasnt on the same page then it maybe a fools errand.
12-17-2008
You can't simulate temperature differences in the way you're hoping. Not without controlling the temperature of the air.
If you wanted to get around this issue in the winter, you could run a open cone during winter and a CAI during summer. Should stabilize things enough to a roughly similar IAT. This is why cars come with such a rough tune. They have to account for everywhere the car might be operated, and account for production variations, all without changing the tune.
12-17-2008
Now is when I wish we could stack tunes in the PCM and use a switch or something to change to them on the fly.
12-17-2008
Yeah, Sabre, I was thinking about trying that; may not lead to a semi-perfect solution but should help.
12-17-2008
no, what youre thinking of is a happy knob. i have both a happy knob and an AFC. the AFC just allows you to scale the MAF to make fueling changes. it also helps with people that are outflowing the MAF so they can scale it down. the happy knob allows you to change the IAT reading through an adjustable resistor (potentiometer basically). usually people with a happy knob unlock their timing tables so that each different setting uses a new timing table so they can increase/decrease timing on the fly. using it just as a temperature variable is just plain stupid.
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