I've used one, and built my own electronics. I assume you were talking
about the less expensive types based on a generic O2 sensor, not the
wide-band, high-tech, super expensive type Myles mentioned. They all
work equally well, or equally bad, depending on your opinion of this
type of A/F ratio meter. The most common type has a row of 10 LEDs,
with 3 red at one end (lean), 3 yellow at the other end (rich), and 4
green ones in the middle. These units sell for $50-150 depending on the
source. AFAIK, all are based on the same technology, and even the same
IC. It's the National Semi 3914N. The design is basically right out of
the National Semi databook. If you're crazy like me, and want to build
your own, here's a schematic:
ftp://ftp.team.net/misc/o2meter.pdf
The advantages of my design are:
1) A regulated, overvoltage protected power supply. (I blew out one IC
using somebody else's unit!)
2) A precise way of calibrating the unit to get the stoich point in
the middle of the display. (This may be the chief failing of the
commercial units.)
The cheapest and easiest way to add the sensor to your exhaust is using
what's called a spark plug non-fouler. Get the 18mm gasket-base non-
fouler, cut the male threads off, bore out the center, if needed, then
weld to the manifold, as close to the motor as possible, but after all
pipes are joined. Use sensor-safe anti-sieze on the sensor threads. You
can also get an 18mm drain plug to block off the bung hole when not
using the O2 sensor, or just use an an 18mm gasket base spark plug.
Generic O2 sensors come in 1-wire, 3-wire, and 4-wire flavors. The 1-wire
is just the sensor, with one end grounded to the body. The 3-wire adds a
heater that gets the thing up to temp faster. They all only work when hot.
The 4-wire is the same, but the sensor is isolated, so you need to ground
one end of the sensor.
Jack W Drews wrote:
>
> I'd like to get a fuel-air gauge to help with tuning my carbs -- the
> kind that operates from an 02 sensor. With unleaded gas, reading the
> plugs and exhaust pipe are less meaningful than they used to be, and my
> EGT gauge is only a partial solution to my desire for data.
>
> There are several on the market, and I've been able to find a little
> info on the net, but not enough.
>
> Questions:
>
> 1. Have any of the listers used one of these?
> 2. Any comments on which ones are junk and which ones actually work?
> 3. Anyone have any internet sites in their bookmarks that would be of
> help?
>
> --
> uncle jack
> (studiously engineering myself to the rear of the pack)
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