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There have been some misleading recommendations regarding the correct ECU pin to use for the A/F gauge floating around lately. I received the correct STi ECU pinout sheet from Dan at godspeed.com today (THANKS, Dan). The correct ECU pin wire to use is connector B137, terminal #25. It is a white wire. It is NOT B134, #26 (this is the signal terminal for the TGV). The correct terminal is for the REAR O2 sensor signal, not the front O2 sensor. The front O2 sensor reads in a very wide voltage range (which most A/F gauges can't read- short of the EXPENSIVE wide band gauges) while the rear O2 sensor reads 0-0.9 V (which the more commonly seen A/F gauges display). This also makes the cheapo A/F gauges completely worthless, as the gas being monitored is quite a ways downstream. The computer only uses this rear O2 sensor signal to monitor cat-converter efficiency, while the front O2 sensor reading is used to adjust A/F ratio. In essence, the signal from the rear O2 sensor only serves to light up the pretty LEDs in the gauge rather than provide any useful information. Either way, I hooked up my Autometer A/F gauge because I had an open spot in my gauge housing and figured the gauge looked better in the vacant spot of the housing than it did sitting idle on my garage floor. Let me know if anyone wants a copy of the ECU pinout.
 
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