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Old 12-07-2004, 11:47 PM   #1
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Dr. jay as soon as i can get around to scanning my car which will likely be saturday if i dont get anxious about it and do it sooner ill start this thread. IN the mean time i have a few questions:

An afc just changes the maf freaquency right? so wouldnt the fuel system respond to that and richen or lean out the af mixture accordingly, or would the it try to change the ammount of air coming into the motor to accomadate for the ammount of fuel your trying to add or take away?
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Old 12-07-2004, 11:54 PM   #2
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It changes the maf frequency and load variables so your transmission will shift a little different (not at WOT) but anyways
It just richens or leans the mixture and depending on your setting, the computer may compensate for it beign too rich or too lean.
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Old 12-12-2004, 12:58 PM   #3
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Ok finally got around to scanning my car today and here is what i found. First off i think it is important to point out that im not running a 2.2 inch pulley, its around 2.5 inch. What i did is start the car and let it warm up, then scanned it. here is part of what i found.

AFC was tuned at 92 percent and the car was turned off
LTFT=127
LTFTCL=1
STFT=112
Closed loop status
Spark adv.=18
AFR=0

i then turned the car back on and got this
AFC tuned at 92 percent
LTFT: 135
LTFTCL:1
STFT:128
Open loop status
Spark adv.:19
AFR:0

What does this tell me and is there anything else i should include that would give me more info?
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Old 12-12-2004, 05:32 PM   #4
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Quote:
Originally Posted by jachin
Ok finally got around to scanning my car today and here is what i found. First off i think it is important to point out that im not running a 2.2 inch pulley, its around 2.5 inch. What i did is start the car and let it warm up, then scanned it. here is part of what i found.

AFC was tuned at 92 percent and the car was turned off
LTFT=127
LTFTCL=1
STFT=112
Closed loop status
Spark adv.=18
AFR=0

i then turned the car back on and got this
AFC tuned at 92 percent
LTFT: 135
LTFTCL:1
STFT:128
Open loop status
Spark adv.:19
AFR:0

What does this tell me and is there anything else i should include that would give me more info?
Well in the first list it says you're running a little rich and the computer is compensating. The second is in open loop, so the ST trims default to 128. Thats because in open loop it doesn't listen to the o2 sensor, so no corrections are made. BTW, the AFR will always read 0 because you don't have a wideband o2. Thats about all the useful information you can get from that.

FYI - Middle ground on ST trims are 128. The higher the number the more lean you are, the lower the number the richer you are. Think of this as the pulse width the computer is telling the injectors to fire at. Higher = Pulse longer because any lower and there isn't enough fuel. Make sense?

o2mV would also be helpful, cruising and idle.
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Old 12-12-2004, 06:53 PM   #5
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Quote:
Originally Posted by 95naSTA
It changes the maf frequency and load variables so your transmission will shift a little different (not at WOT) but anyways
It just richens or leans the mixture and depending on your setting, the computer may compensate for it beign too rich or too lean.
As I understand it, it ONLY changes the MAF frequency. This being the downside of using it. Its only affecting one sensor. Meanwhile load is calculated by the MAP sensor, TPS, and RPM.
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Old 12-12-2004, 07:06 PM   #6
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Quote:
Originally Posted by DrJay
Quote:
Originally Posted by 95naSTA
It changes the maf frequency and load variables so your transmission will shift a little different (not at WOT) but anyways
It just richens or leans the mixture and depending on your setting, the computer may compensate for it beign too rich or too lean.
As I understand it, it ONLY changes the MAF frequency. This being the downside of using it. Its only affecting one sensor. Meanwhile load is calculated by the MAP sensor, TPS, and RPM.
The MAF frequency is a variable for determining load.
When i stray too far off from 100% my partial throttle shifts change.
Also with the 4t65'* the maf signal is a variable for determining line pressure.
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Old 12-17-2004, 08:51 PM   #7
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How could you tell that the computer was compensating for running rich? what does LTFTCL stand for? Ill scan it tomorow and check out the o2mv. thanx
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Old 12-17-2004, 08:53 PM   #8
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Originally Posted by DrJay
Ok finally got around to scanning my car today and here
FYI - Middle ground on ST trims are 128. The higher the number the more lean you are, the lower the number the richer you are. Think of this as the pulse width the computer is telling the injectors to fire at. Higher = Pulse longer because any lower and there isn't enough fuel. Make sense?
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Old 12-18-2004, 02:55 PM   #9
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O2 sensor was at around 450 at idle, and when i was cruising it was around 750, the highest i saw it get up to was 813 at WOT.
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Old 12-19-2004, 04:52 PM   #10
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So for the most part, everything checks out. IM going to see about leaning the afc out a little bit next weekend, i dont really have the gas or money to do this right now. Out of curiosity how high and how low will the fuel trims go? I also want to start messing with the afc in advanced mode but im not really sure how to tune it, the fuel curve should be a gradual slope right THen the only difference between stock and aftermarket injectors is that basically the holes are bigger, and i need to use the afc because if they were to fire at the same rate as the stock injectors, it would deliver more fuel than what it needs right? When im tuning the afc, im tuning it to 92 percent of which maf peramiter?
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