Turbo XS Unichip Harness Mod

The Turbo XS Unichip system is easily one of the best ways to unleash more power from your WRX, but many of the owners of the Revision 3 T-harness boards were experiencing some hesitation under low throttle conditions (>40%) from low revs (2500+ RPM).  Thanks to the guys on www.i-club.com and some careful and well though out research, the TXS Unichip community has come up with a fix for the problem.  It seems that on Revision 3 of the T-harness board, one of the most popular, Turbo XS has chosen to enable the chip above 40% throttle.  However, this was leaning out the air-fuel mixture too much, and causing high Exhaust Gas Temperatures, and some hesitation.  The solution is simple however, change the reference voltage resistor on the board and raise the throttle position level that enables the piggyback ECU.

To complete this task, all you will need is a 1/4 Watt 22,000 (22k) Ohm resistor, and a soldering iron with a fairly fine tip.  I don't recommend replacing the resistor on the board, but adding this to the back.  The resistor you are working with is labeled as R8, however the resistor itself hides the label.  So, look closely at the pics, and solder the resistor to the back of the board.  Neat and Tidy!

The Location of R8 on the T-Harness board

A close up of the resistor.  You are looking at the one closest to the black 16-pin IC

The back of the board.  Follow the pins from the 16-pin IC, and the next in line, between the two thick traces is where you a going to be working.

My good friend Kevin Hoare prepping the resistor for installation.  He handled the soldering while I took care of the photography for you guys.

We put the resistor in place after shortening the leads, and held it there using a large Allen key.  Kevin applied the perfect amount of heat and solder to make a solid connection.

A close-up of the resistor soldered in place.

The entire side of the board, with the new resistor in place.

This is the T-harness board back in place next to the Factory ECM.  You can see there is plenty of clearance, and no chance of shorting.

 

NOTE: If you are not experienced and confident with a soldering iron, please ask a friend to help you.  You don't want to damage anything, especially the traces on the T-harness board.  If you don't have any friends, almost any local electronics (TV. VCR) repair depot or reputable car-audio shop can give you a hand, and shouldn't charge you very much.

Happy Driving!!!