WEGO sensor problem

[James H]

So it looks like the EGO ground should be on the engine, not the sensor return, is that correct? That's how I have mine connected. I'm using an LC-1, and I can't seem to get any reading on the TunerStudio other than 7.40AFR. I've set up the project properties for the LC-1 as well as calibrated the AFR map for it. I've checked the voltage coming out of the LC-1, and it is 5V. I've calibrated the heater and sensor according to the instructions from Innovate. If I plug in their data logger program, it reads ~20:1AFR. The sensor ranges are the default from the factory.

Does anyone know:
1) Why am I getting 5V from the LC-1 in free air
2) Why might TunerStudio show 7.4AFR (which is the reading you get for 0V)

Everything else seems to be working, and I fired the engine up and it ran OK, so now I should be ready to start tuning if I can figure out my O2 problem!

[Matt Cramer]

The LC-1 should be grounded to the block as this is a power ground, and should be putting out 5V in free air. The question is what TunerStudio is doing. Did you calibrate it for the LC-1 default under Tools -> Calibrate AFR Table?

[James H]

Yes, I calibrated the AFR map using the LC-1 default settings option. I also thought that free air would be a high reading, but less than 5V since free air isn't 22:1 but closer to 20:1. Using Logworks, I see a reading of 20:1. I'm thinking about using a AA battery or something to connect to the MS input to see if that gives me a different reading. If that doesn't work, it sounds like there may be a problem with the ECU.

[Matt Cramer]

Free air is about 20% oxygen, so it's way more oxygen than 22:1. It's off the scale, and when the wideband goes off the scale on the lean end, it goes to 5V output.

[James H]

Thanks Matt, when I looked at the Logworks display it says ~20:1, but this is in the exhaust pipe also so it's probably different. I've been digging further into the issue, and took the board out to verify 5V on the processor pin (which was there). Then I decided to reflash the FW on the Megasquirt. After that, it reads 18.0:1 solid. So I plugged back into the LC-1 to just change the voltage outputs to see if I could get a value different than 18.0:1, but it seems like when I do that the LC-1 needs to go through a full heater and free air calibration to work again, and after that the Megasquirt goes back to reading 7.4:1. Another re-flash gets it back to 18.0:1. Somehow the LC-1 glitching out seems to corrupt the FW on the Megasquirt. So I've got the LC-1 back to factory defaults, and the Megasquirt freshly flashed and reading 18:1, and I'll try to start it tomorrow or Sunday and see if the AFR changes.

Have you heard of any issues like this before?

[James H]

Well I'm still having O2 sensor issues. Went to start the engine, and found that the reading was 7.4:1 again. Re-flashed, and it went back to 17.0:1 (but strangely not 18:1 as it had previously been doing). Had to turn it off to put a fuse back in (not related to MS), and turned it back on to see 12:1. I started it up, and it is solid at 12:1, never moves at all even though I opened the throttle. My last idea is to try hooking a AA battery up again after disconnecting the O2 sensor from that pin and re-flashing. If that doesn't work, is there anything else it could be but a bad processor? I've checked the voltage on the processor pin and found 5V there despite the 7.4:1AFR reading, and I can't find any other places where the O2 sensor needs to be set other than the project properties and calibrating the AFR table.

[James H]

As a last test, I pulled the O2 wire out of the connector and hooked up a voltmeter to it. Prior to starting the engine, it read about 5V. After I started the engine, it read around 2.5V (some bouncing around between 2.4 and 2.6 really). It looks like the Megasquirt isn't working then. I'm actually using an MSII-Sequencer. I guess I can either try to get it repaired somewhere or upgrade to the MS3-Pro.

[Matt Cramer]

Please make sure the O2 sensor type is set to Wideband under Project Properties, and that you've sent it the LC-1 calibration under Tools -> Calibrate AFR Table.