Piggyback Heaven – Installing a VAFC in a Acura RSX

Today we’ll be installing a VTEC Air Fuel Controller part number 401-A015, otherwise known as the VAFC for this supercharged Acura RSX. Running a CT Engineering supercharger kit, but opting to leave out the programmed ECU, we’ll be installing a VAFC to round out the RSX’s fuel trims before going full blown AEM EMS standalone.

Why install the VAFC? This controller will allow us to fool the PCM into adjusting the fuel trims and move the VTEC engagement point wherever you wish. While this isn’t a long term viable solution, it’s more than enough to get us on the road until the standalone is installed.

Tools required for this job

Electrical Tape
Wire strippers
Wire clips or Solder iron

Before starting on this job, you must first read and review your VAFC installation booklet and familiarize yourself with the wires and the sequence in which they are installed. Now make sure to print out the ECU pinouts, shown here :

The wires you will be referencing for this job are :


  • Red Power
  • Yellow / BlackBrown ( Secondary Ground )
  • Black ( Primary Ground )
  • Gray ( Throttle Signal )
  • Red / blackOrange ( TDC Signal )
  • Blue / WhiteLight Blue ( VTC Cam Signal )
  • GreenYellow ( ECU Side of pressure signal output )
  • Green / RedWhite ( Harness Side of pressure signal output )
  • Greed / RedPurple ( ECU Side of VTEC Solenoid signal output )
  • Green / YellowPink ( Harness side of VTEC Solenoid Signal output )
  • Green / YellowGreen ( RPM )

First pull up on the passenger side seat lever and slide the seat as far back as it allows you to go. Next look towards the passenger side floorpan and pull back on the carpet until it gives you access to the ECU cover and panel.

You will see 2 pin buttons, pull those push pins out and pull off the cover to expose the ecu.

Now you unplug your ECU harness

Now, source the green / red wire on the 31p plug of your ECU wiring harness and cut the wire. Make sure to leave plenty of slack on either end of this wire. Now, solder the yellow VAFC wire to the ECU side of the pressure signal pin, and then connect the white wire to the harness side of the pressure signal pin.

You can elect to use the Apexi supplied bullet connectors as I did here, as this VAFC install is not permanent. If you intend to rock the VAFC for any extended period of time, I would recommend soldering the pressure wires to maximum reliability.

Next it’s time to tee into the power by locating the power wire located on same 31p harness. Source your two VAFCII red power wires to the yellow/black ecu power pin on the 31p plug.

Now locate your black and brown wires ( ground and secondary ground ) on the VAFCII harness and splice them into your ECU ground pin, found again on the 31p plug. Be sure to take care when soldering these two wires in, as they must be an inch apart and the BROWN wire must be soldered closest to the ECU side of the harness.

Now connect the gray VAFC throttle wire to the red/black TPS pin located on plug 31p.

Then connect the orange VAFCII wire (VTEC CAM SIGNAL) to the green wire located on plug 31p

Now connect the blue VAFCII wire ( TDC ) to the blue / white TDC wire on the ecu plug on the ever popular 31p plug. The green VAFC II wire tees into the one lonely RPM signal on the 31p plug on the opposite end of the harness.

Set your sensor number setting and number-of-cylinders setting through the ETC section of the Menu, along with VTEC type setting, throttle sensor voltage checking, throttle sensor type setting in TH-POINT.

If this is a fresh install, make sure to closely follow the throttle opening learning found in your VAFC manual under “Initial Setup”

Dont forget to set the reference cam angle for vehicles with an i-VTEC.

Congratulations! You’ve now installed a VAFCII into your I-VTEC equipped K20 motor! Happy Boosting!


2 thoughts on “Piggyback Heaven – Installing a VAFC in a Acura RSX

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