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How exactly does it work? Does it only affect WOT readings, or does it end up affecting the way the car runs period? Since I have a FWI, should I be running a MAF Translator? How would I know if I needed one? Any help appreciated :)
 

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Hey there. Honestly, i'm just learning about it myself as I need to get this all straight to fix my problem.. That being said, I posted a Thread posted in "PCM'S and TUNING" column just above here called "O2 Sensor values, LTFT/STFT". Regardless of my problem, i've recieved a couple of replies regarding the operating principles of the AFC version 1.1 and 2.0. Hope this will get you started anyway. Good luck. :cool:
 

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It only effects the AF ratio when the MAF sensor is used. Mainly WOT or close to it.
 

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1998 GTP coupe. Stock and rust free. Totaled @ 87K miles
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hvactech said:
How exactly does it work? Does it only affect WOT readings, or does it end up affecting the way the car runs period? Since I have a FWI, should I be running a MAF Translator? How would I know if I needed one? Any help appreciated :)
You know the PCM using MAFF, IAT, and ECT to lookup the base IPW in the fueling table. The table cals are based on the factory designed intake and pulley, so when you switch to a CAI and a smaller pulley you upset the balance of the fueling cal. So you can trick the PCM into see more or less air than in the calibration table to adjust the fueling.

The AFC 1.0 is a small microcontroller that scales the MAF frequency (MAFF) by a percentage you set with the switches. The v1.0 has 8 switches like a binary counter:

128 64 32 16 8 4 2 1
ON
OFF

The percentage scaling you get is the sum of the ON switches. Example: if switches 64, 32, and 2 are ON and all others OFF, you get 98% scaling. So if the input MAFF is 1000 Hz, the AFC will scale this to 980 Hz.

the v1.0 scales the same across the entire 0 to 11,500 MAFF range. So in the above example you will always scale 98%. When idling typically 2500 Hz, the PCM will "think" the MAFF is 2450 Hz. When WOT at 10,000 Hz, the PCM will see 9800 Hz.

Let's say during a WOT run, your O2s are a little lean. You can set your AFC to add fuel (say, bump 103%). But the v1.0 scales across the whole range so even at idle and cruise it will be biasing the MAFF. In closed loop mode this shows up as negative LT fuel trims. But it's desired to keep the LTFTs to near zero because the last LTFT cell is used to bias the WOT fueling. You also run the risk of setting the AFC too high, and maxing out the MAF table (remember the table goes up to 11,500 Hz, so if you are really flowing 10,500 Hz and you set above 109% you will max out the MAFF the PCM is seeing. This will cause big problems and probably cause you to pop a piston.)

the tranny line pressure is also determined partly by engine load, of which MAFF is an input. So if you have a v1.0 and you are set above 100%, you may have harder shifts during normal cruise. Or if depending on your mods/tune (say larger injectors) you are set at less than 100% your tranny may shift softly or cause driveability problems.

The AFC v2.0 is different because you can scale according to MAFF decade (1Khz, 2Khz, etc up to 13 KHz). So at idle and cruise you can set the MAFF scaling at 100% (no scaling) or fine tune your trims and then only bump up at WOT (above 7Khz)
 
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