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Air fuel ratio meter gauge

Below on this page there are bar graph air fuel ratio meters that aren't the most common types, like the more typical gauges. There is a lof of information to find on the internet and some links are the oxygen sensor page.

Is like a little Oxygen Analyzer or Exhaust Gas Analyzer

Well in a little way. Even though a wideband o2 sensor should be used for accurate readings, it is not always needed. Other types of related equipment can provide further information, like using an better oxygen analyzer or exhaust gas analyzer to check combustion emissions and then you might think of the catalytic converter.
As mentioned elsewhere, when the air fuel ratio is about ideal and slightly lean, it will allow the catalytic converter to operate at maximum efficiency thus reducing emissions.
An oxygen sensor that has become defective or even damaged may lead to an increased fuel consumption, increased emissions and also decreased power.

When Boost Gauges are used to monitor when and how intake manifold pressure levels are affected or changed, then the air fuel ratio is also affected. With too less fuel at boost, the mixture gets lean, as it shouldn't be. Therefore, an air fuel ratio meter provides additional control.

Air fuel meter gauges for narrow band oxygen sensors, are very useful. They can be always connected since the oxygen sensors they monitor are always there.
All air fuel meter gauges below are to be used with narrow band oxygen sensors.
These sensors are already existing in all cars since around 1980, in the exhaust manifold, or they can be installed in an exhaust header.

So, the 10 led units that are most common are probably calibrated in 100 mV steps ie 100mV, 200 mV, 300 mV and so on.
Some points;
- The value scales of the gauges below are not realistic, since the exhaust gas temperature affects the output voltage areas of a narrow band sensor, in the lean and rich areas. Only the mid stoichiometric point (lambda = 1) output level from a sensor is quite temperature independent.
- The output from an o2 sensor isn't linear, the output voltage switches fast across the middle. In spite of this, none of the meters are designed with that aspect in mind. If the lean and the rich area would have been monitored more in detail, relatively, the number of leds would have to be more in the low lean area and the the upper rich area. Hence, 1 led would be sufficient for the middle 'lambda = 1' area (ca 250 - 650mV), since the output switches quite fast between the lean and rich thresholds. However, the average level (lambda 1) can be viewed in somewhat good way (although an internal averaging capacitor in an air fuel meter could have made it easier).
Therefore, a lower threshold of such a lambda=1-led could be set to 250 mV and the upper threshold at 650 mV. Hence, the average level would be [250 + 650]/2 => 900/2 = 450 mV which is the average level that the ecu measures as lambda 1. But since the o2 sensor switches so fast, anything between these voltages is lambda 1.

The led color arrangement that seems to be the most common is: lean:red, lambda 1: yellow, rich:green
used by Efi, Lambda Link, Halmeter, (Split Second, with more colors), Lumenition, J&S and K&N. The Alpha meters also use that but also have red leds above the rich area.

The Edelbrock and Equus use: lean: red, lambda 1: green, rich:yellow
The RSR has an opposite order since the lean area is green. The manufacturer displays it in use for motorcycles.