Scanguage IGN guage, what is good? 40 either is really bad or really good

[jfitzpat]

Originally Posted by cfg83

There is a part of me that wonders if I trained the ECU to "drive lean" as a function of my driving habits.

Doubtful. Too much O2 in the exhaust is bad for the emission control system, so an ECU will generally avoid it.

I suspect that it has more to do with what, exactly, you mean by "digital AFR". One possibility is that the reading only has meaning over a narrow range and these 'lean spikes' are under reported. That is, overrun conditions, which happen a lot when there is a lot of coasting, are not being reported for what they are, free air in the exhaust and injectors closed.

You see a similar misleading reading quite a lot in performance automotive applications. Folks will add a mod on the inlet side for more air, then the points will be out of temp range at low loads. Spark plugs, etc. have a surprisingly narrow operating temp range in their designs. Once temps are too low, occasional misfires occur. Because many 'AFR' gauges are basically putting pump current back into a PID loop, these small parcels of uncombusted mix are not reported as spikes, but instead shift the overall readings lean for a bit.

I've lost count of how many times we've been accused of reading 'too rich', which is actually very difficult to do with our measurement principle. When we actually go out and look at a log instead of just a gauge, we are clearly correct and the abnormal combustion events are clearly visible.

I don't mean to come across as badmouthing other gear, I'm just stressing that you need to know the limits of any instrument. A conventional current based wideband is perfectly suitable for many applications, you just need to know when it will lead you astray. Like misfires shifting the reading lean. If you enrichened based on that false shift, you would probably create fouling and make the misfires worse.

-jjf