Guide: DIY Fuel Cut Defenser

Date: June 5th, 2004
Cost: $15
Time: 30 minutes


  • 10K ohm 0.75W 15-Turn PC-Mount Trimmer 271-343 (potentiometer)
  • Project Box & PC Board Combo 270-283
  • PC Board Terminals 276-1388
  • 15K ohm fixed resistor (15K can be hard to find, but you can string a 5K and 10K resistor in series)
  • Wire (I recommend three different colors)
  • Soldering iron and solder
  • Knife, wire strippers, Phillips screw driver, and other misc. tools


Your goal is to solder all of the components on the board. I recommend mounting the terminals near the center of the board (instead of near the edge as I did). Mount the potentiometer (pot) at one end of the circuit board and then mount the terminals toward the middle of the board, aligning them with the pot pins. You probably have to separate the terminals into two pieces to align them.

The pot has a screw at one end for adjusting the resistance. The pin closest to this screw is called T1. T2 is the middle pin and T3 is the pin closest to the other side. Between T3 and the terminal it lines up with, you want to mount the fixed resistor (or resistors if you are combining a 10K ohm and a 5K ohm resistor). Solder everything in place, then create a trace from T1 to its terminal, T2 to its terminal, and T3 to one end of the resistor(s) (resistors are not directional). If you used two resistors, create a trace between them. Also, create a trace from the other end of the resistor to the terminal. If you are terrible at soldering, you can use small strips of wire to connect the components, but that does not look as nice.

Strip the end of three wires and connect them to the terminals, screwing them down tightly. You may want to decide where you are going to mount the FCD when you are done in order to know how long the wires should be. Generally, one or two feet is plenty, but you can always use longer wire and trim it. I recommend using three colors. T1 is for the connection to the sensor (I used red). T2 is for the reduced voltage to be sent to the ECU (I used yellow). T3 is ground (I used black). An extra step I did was to cut slightly along the side of each solder trace with the dremel to make sure there could not be a short (a short in electronics is when there is a path with no/minimal resistance which causes high current flow).

Before you install the circuit in your car, you want to set the resistance for your boost needs. The small screw on the side of the pot is where you make the adjustment. Connect an accurate ohmmeter to T1 and T2 and adjust the pot as necessary. Since every car is different, you cannot guarantee what resistance level will be necessary to set the fuel cut to a certain value; however, the following figures are a good estimate.

14 psi: 1140 ohms; 15 psi: 1730 ohms; 16 psi: 2340 ohms; 17 psi: 2950 ohms

Install the completed circuit in the black housing (drilling a hole in it to run the wires through). I cut the posts that the board mounts on in half so that I could mount the board toward the middle of the box. Tighten down the board and the cover.

The FCD is connected between the boost pressure sensor and the ECU. The pressure sensor (black) is at the rear of the engine bay on the passenger side next to the diagnostic box (gray). With the ignition turned off, disconnect the black pressure sensor plug. If the wires are wrapped, remove some of the wrapping to reveal three wires: red w/blue stripe (+5V from ECU - VC), blue (reduced voltage signal - PIM), and brown (ground - E2).

Cut the blue (PIM) with plenty of wire to work with at each end. Connect the FCD T1 (red) wire to the wire connected to the plug. Connect the T2 (yellow) wire to the other side of the blue wire (it runs back to the ECU). Strip some of the insulation from the brown (ground) wire. The black T3 wire should connect to this brown wire (you could use a tap-in connector, but I recommend solder for all wire connections). You should use heat-shrink wrapping or—minimally—electrician's tape to cover the soldered connections. Plug the sensor back in.

Now verify that you did everything correctly and mount the FCD somewhere in the engine bay. Some 3M double-sided sticky pads would work well. You should double check all of the connections to make sure none are loose. That is it!