My O2 gauge is getting some really bad values. I have a dash mounted gauge that seems to be reading correctly but the ECU is seeing values that range from 0.4 to 22 in less than 1 second.

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In fact I disconnected the O2 gauge from the ECU and it was still getting the same signal. I even installed a new O2 sensor and got the same results.


Any thoughts on solving this?

What brand O2 controller? Innovates especially are really sensitive to issues with the sensor grounding.

Bosch 17018

That's the oxygen sensor itself. Microsquirt cannot read the low level voltage signal or run the heater so there is a controller in the middle (innovate lc1, 14point7 spartan, etc.) that handles that stuff. I'd bet your problem is in the ground wiring of that controller. Spurious noises signals doesn't seem like an O2 sensor element problem.

grounds...

rich

OK so I am no expert when it comes to chasing down where the electrical pixies go.

But for the Micro squirt, it uses a common ground for all of the sensors that feeds back into the ECU to prevent grounding problems. The coolant, intake air temp, MAP and O2 sensor all use the same ground.

These seem to be function correctly and that ground is internal to the ECU so there is no way to alter or improve the ground.

The O2 sensor is function correctly as indicated by the dash gauge and there was previously reasonable agreement between the ECU O2 reading and the gauge.

With the O2 sensor completely disconnected from the ECU it is still getting a signal that is exactly the same signal and wildly fluctuating reading that I see with it connected.

So this indicates to me there is something in the ECU that is not right.

Your O2 controller should NOT ground through the ECU. You're correct about the MS having a dedicated sensor ground. But the O2 sensor isn't technically a 'sensor' in this context, because the MS can't talk directly to the part in the exhaust, there is another controller that acts as an intermediary. That controller has it's own power and ground wires, but these aren't sensor power or ground. It's a subtle distinction, but important.

The O2 sensor controller is also powering a small heater element in the sensor. This takes a fair bit of power, and the ECU ground shouldn't have to deal with that much power.

The O2 controller should ground to the same place as the ECU grounds (Pins 22 & 23). Usually these ground to the engine case, but yours may be elsewhere.

Correct the heater portion of the O2 sensor should and is not grounded through the ECU.

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The separate controller and ground in the sensor appear to be ok as indicated by the proper operation of a dash mounted digital readout that came with the O2 sensor.

As shown below, the gauge/controller has a 0-5V output that sends a voltage to the ECU which is set up to read on a linear calibration scale.
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That 0-5V output is going to Pin 34. However when I disconnect that wire from the ECU it is still getting a signal. It still gets a signal when I unplug the O2 wire harness from the sensor and there is no power to the gauge/controller which would have to mean no signal on the 0-5V output.

This configuration ran for over a year for my 2056 so I know it works. Could be a wire issue but with all of the O2 related wiring disconnected from the ECU and it still gets a signal for O2 it is hard to think of another place it could be picking up that signal.

a short in the ECU or aliens

Did you configure the microsquirt controller for and setup the AFR tables for a 0-5V input WBO2?

Yeah, if you've disconnected the O2 and are still getting noise it could be a ground loop issue, damage inside the ECU, or aliens.

Yep was running very well until this issue came up.