How to Tune a Honda With a V-AFC


The APEXi VAFC is a piggyback fuel tuner intended for Honda applications. The VAFC works by modifying the stock oxygen sensor signal that is sent to the engine control unit (ECU). The ECU uses this signal to constantly monitor the air/fuel ratio, making fuel adjustments when needed. The VAFC allows you to input correction values for the stock oxygen signal, which will effectively increase or decrease the amount of fuel injected into the engine. Before tuning your Honda with the VAFC, you need to install an air/fuel ratio gauge or data logger device in order to view your engine's air/fuel ratio. This ratio will be used for tuning purposes with the VAFC.

Things You'll Need

  • Air/fuel ratio gauge or data logger
  • Passenger
  • Find a safe, legal roadway on which to accelerate your vehicle to redline in second or third gear. Take a passenger with you so that he can safely monitor the air/fuel ratio while you operate the vehicle. Ensure that your air/fuel ratio gauge or data logger device is powered on prior to accelerating. Also, data loggers can be set to record numerous engine parameters; so if you are using a data logger, ensure that it is set to record the air/fuel ratio of your engine.

  • Accelerate your vehicle to redline. Have your passenger monitor the activity of the air/fuel ratio gauge or operate the data logger. Once the engine has reached redline, let off the throttle and continue to drive normally. Find a safe place to park so that you can begin tuning with the VAFC.

  • Power on the APEXi VAFC. Use the dial to navigate to the "Hi/Lo" throttle setting menu. Select the "Hi" throttle option, and the VAFC will present you with a bar graph. The bottom line on the graph represents the vehicle rpm value, and the bars are the current oxygen sensor correction values. The default correction setting is 0% for all rpm values.

  • Use the air/fuel ratio information your passenger gathered from the air/fuel ratio gauge or data logger to tune the VAFC correction values. The stoichiometric air/fuel ratio for internal combustion engines is 14.7/1. However, for optimum performance and reliability, the air/fuel ratio should be slightly rich across the rev range, generally around 13.2/1 for naturally aspirated applications, and 12.5/1 for forced induction applications. The optimum air/fuel ratio setting will vary slightly depending on vehicle and atmospheric conditions, so you will need to run multiple tuning sessions in order to perfect the air/fuel ratio for your particular vehicle.

  • Use the dial on the VAFC to increase the fuel correction percentages at any rpm values that produced an overly lean air/fuel ratio. Likewise, decrease the VAFC fuel correction percentages at any rpm values that produced an overly rich air/fuel ratio. Only increase or decrease the correction values by a few percent at a time. Then, repeat Steps 1 and 2 to monitor the new air/fuel ratio values your engine produces. Repeat the tuning process until you achieve an optimum air/fuel ratio across the entire rpm range.

Tips & Warnings

  • Have your VAFC professionally dyno-tuned for even better results. Tuning on a dyno makes for more stable atmospheric conditions and air/fuel ratio monitoring. This will allow you to achieve the most efficient and reliable VAFC tune possible for your Honda.

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