2G AFC tuning for dummies.
To find low settings, do this:
With the car turned on and parked, rev to 1k. Log short term and long term fuel trims. Add the two
together, and that is how the ECU is modifying fuel delivery. If short term is -2% and long term is
+4%, then you are currently getting +2% modification to the fuel delivery. Therefore, your 1k Lo
Throttle AFC setting should be +2%. Do the same for 2k, 3k, and 4k. Average the settings, and run
them across the board.
So if after doing 1k-4k, you end up with 1% 3% 2% 2%, make 1k-8k all 2%. Then go out on the road and
do it again, with someones help of course. At this point you are putting load ont he engine which
changes fuel delivery. This lets you fine tune the settings.
There is a switch over somewhere in the RPM band, I think it is around 5500, where fuel trims are shut
off. So, you can really only do the lower Lo throttle settings. That is why you average and paste them
across the board.
Lo Throttle does not have to be perfect, either. The ECU is still controlling fuel at that point, so
you just want ot get them relatively close. For me, all of my lo throttle settings are just -10%
across the board.
For Hi throttle, you get your baseline by doing pulls in 3rd gear on the freeway. Don't worry about
1k and 2k. Figure out 3k-8k and then use your 3k setting for 1k and 2k.
To determine a RPM points setting, start about 500 rpm before it and floor the throttle. Run it through
till you are 500 rpm over the throttle point. Watch your o2's. Assuming your o2 sensors are properly
warmed up (drive around for 10 minutes first) you want your o2's to be about .94.
This leaves you a tad rich, and in a good place to do fine tuning.
To fine tune, you need to log RPM Timing and O2. Do pulls from 3k to 7.5k. You should see 10 degrees of
advance when boost first hits. From there, timing should never drop and hopefully, it should never
hesitate to increase either. You want a nice steady incline. Graphing out your data helps me to
Good timing should end up in the 20-22 range. I have heard of people hitting as high as 24.
If you do any testing, you might notice that peak power is not made with full ECU awarded timing advance.
You will make more power running a bit lean and getting less timing (say, 17 degrees) than you do at 21.
However, getting the ECU to award full timing advance means you are running safely, which is
much, much more important on the street than maximum power.