WBO2 shows lean, engine rich, NOT misfiring?

[elaw]

So here's an interesting one. Does anyone know of a condition that could cause a wideband O2 to read lean when the engine is running very rich but not misfiring?

Here's 1000 words that show what I'm seeing:

graph.png

That's right after start... the engine is running very rich, the AFR shows rich, then suddenly goes full lean. I know a lean misfire can cause that but the engine does NOT seem to be misfiring! Regular misfires are very noticeable on a 5-cylinder engine, and you'll also note that transitioning in/out of the indicated-lean area, there's no big change in MAP that would be associated with losing or gaining a cylinder.

The sensor being used is a 14point7 Spartan... the first-gen one with the sensor permanently attached. I've confirmed the rich condition is the cause of what I'm seeing, as when I started the car this AM I dramatically reduced ASE and this didn't happen.

Has anyone else seen this kind of thing before? I don't think it's a Megasquirt problem... more likely either something with the sensor or something with physics. Unless there's a glitch somewhere that causes a full-lean reading when the sensor is outputting 0 volts - my sensor is 0V = 10 AFR, 5V = 20 AFR.

I'm attaching two log snippets - one corresponding to the graphic above, the other a much longer illustration of the same thing.

I'm not attaching an .msq file since I'm using customized firmware - it's based on MS3 v1.2.3. But I definitely did NOT change anything related to AFR sensing! If anyone does want the .msq I can attach it but you'll have to use my special .ini file to read it.

[racingmini_mtl]

It seems to be going out of the AFR range the Spartan can report. You might want to inquire with 14point7 what happens then. It might be how the controller responds to an out if range situation. Or it might be a controller failure.

Jean

[elaw]

I was thinking it could be something like that. I've posted a message on their support forum - I'll post back here if I get any info.

I never noticed this problem before, but going back and looking at old logs it seems like the AFR never went below 10.0 before. I've been increasing ASE lately to get more fuel on the walls to correct a lean condition that happens the first time you hit the gas after a cold start - it looks like I may have gone a little overboard with that.