1991 Turbo Miata (SpeedyEFI ecu)
Recently I went for a drive and it all of a sudden started going lean. It goes lean mainly in cruise areas and sometimes at idle. I ended up changing the fuel filter and fuel pump strainer, which didn’t fix it. I then redid the wiring for the Wideband (AEM x-series) and still am not receiving a reading in tunerstudio. I’m positive that all the wiring is correct, is it possible that the o2 sensor itself needs replaced? I’d love to hear some ideas. Thank you for your help!!

-Jacob

 

Did you delete the factory O2 sensor and then wire the new gauge to send either CANBus or sensor signal to the ECU in place of the factory O2 wire?

 

Yes, I did. Everything was working great for months, after having it tuned. Then this all of a sudden happened.

 

Have you taken a datalog and confirmed that it's only lean during cruise and idle? Is it possible that it's lean under all conditions but you're mostly looking at the gauge when you're idling or cruising?

 

Turns out there was a voltage issue with the sensor, (Bosch 4.9LSU). I ended up replacing it and it was back to normal.