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Disclaimer: I take 0 credit for coming up with this. I merely combined 2 other methods into something that worked for me. This was done in version 4.2.12 because that's the version that my tuner wanted me to use.

FIrst you need to decide how you are going to connect to the AC pressure switch cabling. I unplugged the connector and pinned directly into the plug with spade connectors with one prong clipped-off of a temporary wire to the wideband's analog output. Since you're connecting your wideband's analog data into the ECM this way, you 'll need to use the signal AND sensor ground. I used the AEM 30-0300 X-Series, which uses WHITE for the 0-5vdc and BROWN for the sensor ground. The 0-5vdc (white) connects to the PRESS SENS SIG (GREEN/BLACK) on pin C and the ground (brown) to the LOW REF (TAN) wire on pin A. You can accomplish this with the aforementioned method, or more semi-permanently using relays and a switch inside of the car, or a manual switch at the sensor.
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Now that the hard part is over, we set up the VCM scanner to look for the signal.

For this to work, you need to log AC Pressure Sensor voltage. Right-click the channel list and select "ADD CHANNEL" to add the Channel AC Pressure Sensor; make sure the units are volts.
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Next you need to setup a user math parameter that will take the AC pressure sensor voltage and calculate the AFR based on AEM's voltage output. Select TOOLS>MATH PARAMETERS. Select one of the unused User Maths. I named mine AFR and gave the abbreviation AFR (you can name it whatever you want to). Take this next line and cut and paste it into the Expressions field. Make sure to copy everything including the open parenthesis:

([7101]*2.3750)+7.3125

7101 is the PID the ECU uses for the AC pressure sensor, and the other math gets you a pretty spot-on (with my gauge anyway) AFR reading. IF you find that yours is a bit off, you can adjust for a voltage drop by adding and subtracting from the 7.3125. One of the source threads I referenced below uses ([7101]/.5)+10, but it wouldn't match up for me as well as the above formula.

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Now we add a Chart to display the awesomeness we've created. Right-click in the Chart v/s Time field and select CHARTS LAYOUT. If you have room inside a group, select the group header and select ADD SERIES at the top. If not, add a new group first. I like to limit the display to 4 at a time so I can see things better. Select PARAMETER, and scroll down to the MATHS>USER DEFINED>AFR (or whatever you named it). Set the Unit to "Air-Fuel ratio 14.7 -Gasoline" and the decimals to 2. I entered 20 as the max and 8 as the min, as that's what my gauge displays. You can add a reference line at a target AFR as well.

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Now you can see the wideband's output displayed as AFR in your scanner!

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Make sure that you save the layout, or you might have to do it over again when you close the VCM Scanner tool.

Sources:
 

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Its waaaaaaaaaaay easier if your wideband has an logging output. Most of them do. All you do is plug that logging output into another usb port of your computer or if you only have one usb, you can use a use expander. You add a channel for you wideband (hp tuners supports AEM, Innovate. plx and one other I cant remember). Then you create your histogram. No wiring at all except plugging in the usb. Hp tuners picks it up automatically and will populate your histogram with your afr for rpm and load. This is for the regular hp tuners also.
 

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Ok, so the above comment opened a door that I didn't know existed, and Google showed me some import forums that (kinda) supported it, so i looked a bit deeper, and got it to work. It's not free like the method described above, but at less than $20, it has it's merits, and will be easier to use in the future (and i can log AFRs and use the AC at the same time).

This is one of the cables I used:
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This is the second:
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Now, any serial cable, or pigtail, or bare end should work (in theory), but these are the ones I ordered, and they worked. I have a bare serial female end coming, as i don't like the small gauge wire in this one for longevity and possible voltage drop.

Starting with the installation again, I cut off the male end of the cable and stripped back the wires. You need to connect to Pin 2 for data (BLUE wire from the gauge harness) and pin 5 goes to ground (I used the ground wire for the wideband) as indicated in you instruction manual. I used the AEM 30-0300 and here is that page:
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NOTE: The above picture shows the MALE end. If you have a female end (as I did) the pins are reversed. I have found that if you use a standard cable, Pin 2 should correlate to RED (Data) and Pin 5 to Green (gound).

Now plug the serial cable into the serial to USB conversion cable and plug it in. Some of the resources say that you can use a USB hub if you don't have enough connections, but I cannot confirm that. I had the Hp Tuners cable and the Wideband cable in seperate USB plugs on my laptop.

Now that the hard part is done (again), we go to the VCM scanner to set it up. The setup is similar to the "through the AC" method, with some slight differences.

First, add a channel:
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This time we use an external source (that you just created and plugged into the USB connection).

Then we create the histogram for the AFRs:
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FIrst, select the Group you want it in, then add a new series, and then select the parameter.

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Then select your wideband model under >external inputs>serial port>

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BOOM, you're done. I plan on using BOTH methods to compare the accuracy between them in the future and will report back.
 

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