How To Tune a HKS VPC

How To Tune a HKS VPC


We recently showed you how to install a HKS VPC in a 1997 Toyota Supra Twin Turbo, and today we’ll be covering how to tune it. Our How To Tune a HKS VPC is meant for those users who have already installed the HKS VPC, and need to tune it correctly. The HKS VPC is an older piggyback computer and during the mid 90s helped propel many turbocharged vehicles across the racetracks of their choosing.

As with all of our writeups, this How To Tune a HKS VPC guide should only be followed or read if you are comfortable tuning your engine. Understand that serious or catastrophic damage can occur to your engine and yourself with improper tuning. Like all tuning computers and piggybacks, the HKS VPC is just as capable of blowing up your motor as it is to generate more horsepower in the hands of a bad tuner.


If you are unfamiliar with the process of fine tuning your fuel or ignition maps, or don’t have the first clue about tuning, stop now and read a few of our articles here.


How To Tune a HKS VPC


When you first install your HKS VPC, all the dials should be set to the top position or 12 o’clock for those scoring at home. We will be addressing each adjustment knob and showing you what the knob does as well as how to tune each settings.


Dial #1 – Response

The response dial is the first dial on your HKS VPC and one of the most commonly adjusted dials you will be using. This response is based on fuel delivery and the HKS VPC uses the tach reference as a guide to see what the engine speed is. Turning the response dial to the left is decreasing the fuel delivery, while turning it clockwise is increasing fuel delivery.


If turned too lean your Supra or 2JZGTE may hit fuel cut or experience pre-detonation or engine knock. Turned too rich can cause bogging and fouling of your spark plugs and oxygen sensors.

Dial #2 – Gain

The Gain dial is adjustment dial that tells the VPC how much fuel to adjust, lean or rich no matter what the location is on the RPM band. Leaving this dial at 12 o’clock is recommended until you get a baseline air / fuel ratio reading.

Dial #3 – Idle

The Idle knob helps the user dial in the base idle and can accurately adjust the fuel trim below 1,300 RPM. Do not touch this dial during initial setup unless your car does not want to idle or has a hunting idle due to excess fuel. If the Idle knob does not do anything or has limited impact, check for any existing intake leaks that could cause this issue. Like the response dial, turning clockwise is adjusting the fuel trims richer, while counter clockwise is leaner (less fuel).

Dial #4 – Option Out


The last dial on your HKS VPC is for complimentary tuning computers that can be connected to the HKS VPC, such as the HKS PPC P-CON or F-CON. Turning this dial left or right is the same as Response or GAIN in this situation, and this dial helps provide additional fuel for levels above the stock fuel cut point. If the stock ECU cannot control injectors that are too large, the HKS PFC F-Con controls the injectors after the stock ECU, so the user can enjoy the full fuel delivery.

Troubleshooting your HKS VPC


  • Car Won’t Start – Check all connections and harnesses to make sure positive connection is made
  • Rough idle – Check Air Intake Temperature Sender and Pressure Sender. Improper placement or install of these two sensors can cause serious problems with your HKS VPC operation.
  • Hesitation or bogging – If your car bucks or bogs despite you adjusting the Response and Gain knobs, double check the sensors and where they are installed.


HKS VPC Wiring Check


If you are still having intermittent problems with your HKS VPC, check the following wires for the values listed below.

  • HKS VPC Green Wire – GROUND
  • HKS VPC Yellow Wire – Switched Power
  • HKS VPC Blue Wire – 1.744 volts at atmospheric pressure (Disconnect the vacuum source)

HKS VPC Part numbers


Have an older VPC with components that you are unsure of? or maybe you need a sensor and aren’t sure what the part number signifies? Here’s a cheat sheet to help you find these hard to locate HKS components.

Air temp sensor – 21212-002100

B-Map Sensor – 21212-006100

Sensor Harness – 21215-003100

That does it for our How To Tune a HKS VPC Guide, for more articles, How-Tos and DIY guides subscribe to My Pro Street!