What is an air/fuel ratio gauge?


Similar Questions:
What is an A/F gauge?

An air/fuel ratio (or A/F) gauge is a voltmeter attached to the oxygen sensor signal wire. The oxygen sensor reacts to the amount of air present in the exhaust stream, and provides an approximate indication of the relative amounts of air and fuel in the combustion mixture. It is a useful tuning tool, although limited somewhat by the characteristics of the oxygen sensor it is attached to.

There are many A/F gauges on the market. Those for DSMs usually read from 0-1V, although newer models may measure a restricted range similar to 700-1000 mV.

Because the A/F gauge is merely a voltmeter, many people have adapted existing equipment or built their own, rather than pay retail prices. One such design is provided free of charge by Brad Bauer, and is based (as most are) on the National Semiconductor LM3914 bargraph display driver IC.

Some DSMers have also offered their homebuilt units to other club members at lower prices. These offers are usually temporary.

For technical information on some of the drawbacks and limitations of DSM oxygen sensors, see this post by Dave Mertz; be sure to read the reply at the bottom from Todd Day. Also check out the oxygen sensor questions in this FAQ.

QA #394


Cam Dorland | 95 Eagle Talon
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