http://www.insightcentral.net/encyclopedia/enlaf.html describes how the wideband air/fuel ratio sensor on the Insight works. It suggests that to monitor the output of the sensor, you need a meter capable of measuring plus/minus voltages. That makes a very simple display difficult to implement. However, a meter reading only positive voltages CAN be used, making it very simple and cheap to show what air/fuel ratios are actally occurring real time.
http://www.autospeed.com/cms/A_110625/article.html decsribes in more detail how the sensor works, and how a $20 simple electronic kit can be used to display the output on 10 LEDs. I have chosen to fit only two air/fuel ratio monitoring LEDs to the dash - one that shows when the AFR is at 25:1 (lean cruise) and one that shows when the AFR is at 12.5:1 (full rich).
By using these LEDs, it is much easier to drive more economically because you know what is going on. Monitoring just the instantaneous fuel consumption display is often NOT a good indicator of when you are in lean cruise, especially at low speed or at high speed and climbing slight rises. The rich AFR occurs at high throttle openings, but its implementation also appears dependent on how long you have maintained a high throttle opening (as well as rpm) - the upshot is that you can enter rich mode inadvertently, especially when climbing hills.
I have checked the action of the LEDs against a MoTeC PLM air/fuel ratio meter and the LEDs are always correct in their indication. In fact, they are faster to react than the tail-pipe mounted MoTeC sensor.
As the article mentions, I also run an EGR operation LED - as previously described in
http://www.autospeed.com/cms/A_110555/article.html and
http://www.autospeed.com/cms/A_110581/article.html, I use more part-throttle EGR than standard. This measurably improves fuel economy in urban conditions.
With the three LEDS – lean cruise, EGR and full rich – showing actual status, it is much easier to achieve good fuel economy outcomes. For example, if I am climbing a hill (lots of hills where I live), I will be using too much throttle to be in lean cruise. However, if I don’t use a huge amount of throttle, I can stay in EGR mode, reducing pumping losses. Full throttle will light the rich LED – therefore, when climbing my country road hill when heading home, I want to see the EGR LED on. If I see the rich LED, I’ll change down to get more revs at a smaller throttle opening, often then going into EGR mode. This appears to be different behaviour to that most often suggested.
In short, monitoring the output of the factory fitted wideband sensor is very cheap, very simple to wire into place, and very consistent in its display. It allows people to see what is REALLY going on in terms of actual AFRs being used.
$20 monitoring of air/fuel ratios
