Ed Anderson used the same chip and expanded the dynamic range with this
skematic.

Rob Weinstock wrote:

LM3914's can be chained to provide any degree of resolution you like. IMHO,
it's a bit of a waste of time, since the EGO sensor only provides a
meaningful measurement of "lean" or "rich", with a healthy hysteresis in
between. Any values reported by the display between these extremes are
inferred by the circuit from simple averaging techniques -- it's just
charging a capacitor.

To do this properly, you need a wide-band O2 sensor. Honda uses these on
their latest cars, and they are expensive to the DIY'er. There is another
list on the 'net for DIY EFI folks. They posted about this topic
exhaustively perhaps 6 months ago.

>From an engine tuning perspective, you would probably want to use a real gas
analyzer anyway. And this circuit is useful for detecting when the mixture
is simply lean, which you would want to know in order to avert problems.

Regards,

Rob

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