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What is an AFC? 
What is a Super-AFC / S-AFC?
What is a Super-AFC II / S-AFCII?

Air-fuel converter, an aftermarket tuning computer sold by A'PEXi. It is similar in some ways to the PMS and VPC but is generally considered less elaborate. It has recently been superseded by the Super AFC.

AFC owners should check out the Super-AFC-DSM mailing list on Yahoo! Groups. You need a Yahoo! ID since membership is now restricted. To join, click here.

The original AFC is now known as the "knob-style" AFC. It had physical adjustment knobs on the front for 5 ranges. The "Super-AFC" uses a digital display and pushbuttons to alter settings in 8 RPM ranges, and has separate settings for high throttle and low throttle. The upcoming "Super-AFC II" is similar but adds more RPM ranges and other features to the devices.

Please note that in typical conversation, when people say AFC, they are usually referring to the Super AFC.

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Has anybody ever installed an AFC on a [DSM]?
My AFC tachometer display is wrong! Is there a fix?
My AFC doesn't work right! Is there a fix?

You would already know the answer to the 'install' question (hint, hint) if you had checked the FAQ Locator. The tachometer display will be wrong until you reset the AFC for a 2 cylinder engine. DSMs only have 2 coils for the four cylinders. People who try to install shift lights have the same difficulty.

Those experiencing other problems should look up the on-line documentation on the A'PEXi USA website and the wiring diagrams provided by the Super-AFC-DSM users group.

AFC owners should check out the Super-AFC-DSM mailing list on Yahoo! Groups. You need a Yahoo! ID since membership is now restricted. To join, click here.

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How does the AFC / S-AFC work?

The AFC works by changing the mass airflow sensor (MAS) signal going into the ECU. This signal is a frequency proportional to the amount of air passing through the sensor.

Picky tech-heads will realize that the MAS puts out three signals: air flow, air pressure, and air temperature. The ECU integrates all of these to calculate air mass. The AFC alters only the air flow signal.

Different levels of adjustment to the signal occur for the different RPM ranges. In-between ranges, the AFC uses linear interpolation to smoothly transition from one adjustment level to the next. Thus, if the AFC is set to +10 at 2000 RPM, and - 10 at 3000 RPM, the signal correction at 2500 RPM will be zero.

The Super AFC also has two different correction maps based on throttle position. The "Th" (throttle) points set inside the unit by the user determines the low-throttle and high-throttle boundaries. The AFC also interpolates between the low and high settings at part throttle. Thus, if the low throttle is set at 10% and has +10% correction, and the high throttle is set at 90% and has +20% correction, the correction at 50% throttle will be +15%.

Despite this flexibility the AFC suffers a few drawbacks. It does not "know" the engine load, only engine RPM. For this reason it is hard to tune each gear ideally, since the engine load at any RPM in 1st gear is different than that in 3rd or 5th gear.

AFC owners should check out the Super-AFC-DSM mailing list on Yahoo! Groups. You need a Yahoo! ID since membership is now restricted. To join, click here.

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How do I tune my [DSM] with an AFC?
What are good settings for an AFC on a [DSM]?

Here is the "basic" tuning drill for the AFC, courtesy of Kyle Tarry:

"Ok, for all of you guys who are asking what to do since you just got a SAFC, here's the drill:

FIRST, BUY A LOGGER! Non matter what people say, you cannot maximize the capabilities of your setup without one. And, for the price of a good EGT gauge, a pocketlogger can be yours.

Now, on to the good stuff. Set the SAFC up, with the throttle poits at about 30% and 80%. Spread the RPM points across the rev range from 1000 to 7500 or 8000 rpm.

Start by getting the fuel trims in line. Adjust the 1000 rpm point with the car at idle until you get the low fuel trim in the 100%-115% range. Then, do they same for the mid and high fuel trims while moving in their respective zones. (probably about idle, then slow cruise, then a faster cruise). Once you have them all around 110%, then you can carry those numbers you used across the low throttle map, and also use them on the high throttle map.

Now, you should have the high throttle map set up with the same numbers you used on the higher RPM's of the low throttle map. Make a WOT run, and log it. Now, look at the log, and at every 1000 rpms simply decide if the engine is rich or lean. If it is lean (knock) then richen the AFC up a click or two, depending on the severity of the knock. If it is rich (no knock, good O2's) then lean it out a click. Keep doing this until you have all the rpm points set up to a few % right above where it starts to knock.

That's really about it!"

AFC owners should check out the Super-AFC-DSM mailing list on Yahoo! Groups. You need a Yahoo! ID since membership is now restricted. To join, click here.

You can also check out Road Race Engineering's FAQ page on how to initially tune your AFC, and TMO's guide to datalogger tuning.

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What is the "blue wire mod"?

The "blue wire" modification involves taking the blue wire from the AFC - normally unused on DSM installations - and connecting it to the oxygen sensor. The blue wire is a sensor check connector from the AFC that allows it to display the oxygen sensor reading. Kind of a free A/F gauge. The AFC does not change anything based on this "blue wire" input, it can only display it.

While quite popular initially, evidence is growing that the AFC accessory sensor inputs are not suitable for this kind of connection. Many people have reported that connecting the blue wire to the oxygen sensor artificially lowers the oxygen sensor signal by a significant amount. This is entirely possible since the AFC sensor inputs might not have been designed to be connected to low-power sensors such as the DSM oxygen sensor.

Still, it is a popular modification for those who want an unobtrusive way of keeping an eye on the oxygen sensor without actually using it as a serious tuning tool. Many DSMers scorn the idea of tuning by O2 reading in any case, as it is most likely the least accurate - though most certainly the least expensive - method available.

AFC owners should check out the Super-AFC-DSM mailing list on Yahoo! Groups. You need a Yahoo! ID since membership is now restricted. To join, click here.

The Last Word: This mod is cute, but useless. Use for entertainment value only.

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What is the "MAP sensor mod"?

The "MAP sensor" mod connects a manifold absolute pressure (MAP) sensor to the AFC throttle input. The goal is to make the AFC load-sensitive rather than RPM-sensitive. As the boost level increases, the AFC can deliver more fuel accordingly. For more information, see this VFAQ by Corbin Behnken.

Here is a summary of the mod:

" Lots of questions about this mod. So here is a summary.

Why? Turn the Hi/Lo throttle reference for the NE points on the SAFC into boost references and not throttle position dependent. This makes the SAFC engine load sensitive.

How? Buy 3 bar sensor GM Part # 16040749 at http://www.gmpartsdirect.com/

wire Pin A = Ground - on firewall
wire Pin B = Sensor output, cut the gray wire that previously attached the ECU's throttle position terminal, and wire the sensor output to this wire of the SAFC
wire Pin C = +5v, recommend throttle position sensor wiring harness - turn ignition on and use a multimeter to find it.

The map sensor has special 3 pin weatherpack connector, these are available from the junkyard or the wiring accessory section of any good automotive store. Get the one with pigtail wires, usually these connectors have internals alignment grooves - shave with knife to fit. Splice into your boost gauge (manifold pressure and vacuum are necessary) with a 1/4" tee and run hose to the sensor nipple.

Drive car and observe the voltage on the SAFC that the sensor makes at max boost. Let's say YOUR car makes 19psi boost and the corresponding sensor output voltage is 4.1v , take 4.1 divide by 5.0 (max sensor output) and the result is 0.82 or 82% This is your Hi Throttle NE point on your SAFC. Set the Lo Throttle similarly. I used a sensor voltage of 1.15v, which corresponds to slightly above -5 in Hg. and is usually not seen at 70mph cruise, thus 1.15/5.0 = 0.23 or 23%. The Lo Throttle NE point is now 23%. I am still working on tuning this in. I pick up some part throttle knock under light acceleration, but mash it to the floor and it works very very well. The upper rpm is better than before I did this mod. I will make a VFAQ page for this someday.

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Why does my Super-AFC shows 0% throttle and my TMO datalogger/Pocketlogger show 7-10% throttle at idle?

The S-AFC is set up to accept the lowest reading as 0% throttle. The TMO and Pocketlogger read the throttle setting from the ECU, which knows better. In other words, the S-AFC is wrong. However, this discrepancy does not affect the S-AFC operation in any way, so don't worry about it.

AFC owners should check out the Super-AFC-DSM mailing list on Yahoo! Groups. You need a Yahoo! ID since membership is now restricted. To join, click here.

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Last edited 09/01/06

Maintained by Sean Costall. Changes and suggestions are welcomed!  If you have any information on the answers to any of these questions or wish additional questions, please mail me.

This page is an extension of Club DSM .