5v ref issues, possibly bad ecu?

jason42003 — Mon, 04 May 2026 19:59:58 GMT

So this all started with my evo 9 running rich. It will start hard with a little gas given to it till it can hold its own then runs but very rich (tops out wideband at 11:1). I then checked live data to find that my iat (gm, cars on sd) was at -13c and ect was sitting at -9c, my garage is around +20c (70f). I thought it was the sensors so I replaced both. This brought iat to -7 and ect to 13 so closer but not right. I then disconnect sensors and measure the voltage at the connector for sensors. It is sitting at 4.7v, so then I backprobbed the ecu and those two pins r only outputting 4.7v from the ecu. Best I can tell from the wiring diagrams the 5v ref signal is dedicated for each outside the ecu( probably joined inside ecu but idk that for sure). So I checked all 12v pins on ecu n they all have battery voltage, check grounds to battery neg post and there is only .011 ohms so those look good. The only other weird bit is that my alternator fr pin which according to wiring diagrams is also supposed to be 5v is outputting battery voltage even with the wire clipped at the ecu. Can someone else tell me differently as far as other sensors that may be on the circuit or confirm that my thought process of a bad ecu is correct that would be much appreciated. Thank you.

EvolutionM - Mitsubishi Lancer and Lancer Evolution Community - Evo Electrical / Audio / Security

5v ref issues, possibly bad ecu?