How to work Mini AFC 1.1

Posted: Thu May 26, 2005 9:25 pm Post subject: How to work Mini AFC 1.1

Just picked up a mini afc off a member of clubgp but need help with adjusting it. Also not sure were it goes.

Any help would be great.
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Posted: Thu May 26, 2005 10:09 pm Post subject:

the mini afc v1.1 is used to adjust the MAFF frequency by a fixed ratio across the entire MAFF band (1KHz to 11.5KHz). It plugs in between the MAF sensor and the PCM harness. It only plugs in one way but be careful to not plug the PCM harness side upside down. otherwise the idle will go up and down erratically.

It has 8 switches, which is basically a binary counter

8 7 6 5 4 3 2 1
0 0 0 0 0 0 0 0

1 = 1
2 = 2
3 = 4
4 = 8
5 = 16
6 = 32
7 = 64
8 = 128

So if all switches are all OFF then the counter is zero. If all switches are ON then the counter is 255 (1+2+4+...+128)

Now the AFC v1.1 is really only good for adjusting the WOT A/F ratio.
So set it for 100% first (3, 6, and 7 on = 4 + 32 + 64 = 100%). Then go do a scan. Depending on your O2 at WOT, bump up by 1 or 2% and rescan.

Now this adjustment applied to the entire RPM and MAFF range so it will make your LTFTs run negative. which will lock in a negative LTFT at WOT and tend to bias fuel negative. so it's like a spiral - WOT is lean, richen up with AFC, LTFT is negative, so it pull fuel at WOT. but hopefully the MAFF adjustment makes more impact than the LTFT bias.
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1998 Silvermist GTP Coupe
Bone stock unicorn
1998 True Green Metallic GTP Coupe
Pullied, cammed, intercooled. With a kiddie seat. It once ran a 13 flat.
1998 True Green Metallic GTP Sedan (retired)
Stock: 14.33 @ 96.5
PB: 13.89 @ 101 mph

Posted: Fri May 27, 2005 12:09 am Post subject:

JFYI: In case u didnt know....the target WOT Bank 1 Sensor 1 voltage should be, .915 or lil lower if u dont see any knock.
Also, Like Mike said, you're gonna run lean while cruising, so when u go WOT from a cruising MPH, you're gonna get a fair amount of "burst knock".
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Posted: Fri May 27, 2005 7:26 am Post subject:

Posted: Fri May 27, 2005 10:58 am Post subject:

oops..yeah that sounded bad. OK, when ur PCM is pulling fuel because it IS rich, when you go WOT it'll trip over itself, so to speak....does that make beetre sense? Embarassed

Posted: Fri May 27, 2005 11:00 am Post subject:

Posted: Fri May 27, 2005 12:02 pm Post subject:

I'm saying that -22% is the maximum the PCM can reduce the IPW from the base IPW table before it will throw a code.

From my Tuning Page http://homepage.mac.com/mguzzo/tuning.html

The PCM contains tables that translate MAFF into the fueling demands. The tables are calibrated to the stock intake design.The higher the MAF frequency the more air is coming in and the PCM adds more fuel by increasing the IPW. An AFC or ICCU can be used to re-calibrate the MAFF to your particular mod set and intake configuration.

Injector Pulse Width: The PCM uses the MAFF and engine load (gear, RPM) to calculate a base injector pulse width which is the time each injector is open to squirt fuel into the engine. The base IPW is recorded in tables in the PCM as a starting point. The PCM then gets smart and uses fuel trims to learn and optimize the fuel delivery for performance and emissions. Typical IPW at idle and cruise is anywhere from 2 to 6 milliseconds (ms); at WOT typical IPW is 17 to 19 ms. At an IPW of 21-22 milliseconds a stock injector is static (fully open and flowing as much as it can).

Short Term Fuel Trim: The PCM makes small adjustments to the base IPW using the O2 as feedback. If it sees the O2 sensor lean, it increases the IPW a little bit. If the O2 is rich, it subtracts from the IPW a little. The STFT can range from +16.4% (increasing IPW by 16.4% to add fuel for a lean condition) to -22.3% (decrease IPW to take away fuel for rich conditions).

LTFT is a group of memory cells in the PCM that are used to store certain operating conditions that affect the fueling tables. As the PCM uses STFT to instantaneously adjust IPW to maintain the proper A/F ratio, it will reach limits. Then the PCM will adjust LTFT to re-zero the STFT. The LTFT is a better average of how the engine is performing as a system. LTFT can range from +16.4% (increasing IPW by 16.4% to add fuel for a lean condition) to -22.3% (decrease IPW to take away fuel for rich conditions).
The interesting thing about LTFT is that when the LTFT is negative, it is used by the PCM to bias the WOT fueling curve. Let's say you are have very negative LTFTs at idle and cruise. When you WOT, the PCM will "lock in" the last LTFT value and apply it to the WOT fuel map. This actually ends up taking fuel away and you risk having a lean condition at WOT, which is generally a Bad Thing.

Posted: Fri May 27, 2005 12:45 pm Post subject:

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