AIR FUEL RATIO GAUGE

The Air/Fuel Ratio Gauge is essentially a voltmeter that displays the voltage output of an oxygen sensor in order to determine the richness or leanness of the exhaust mixture. It provides four red LEDs (for lean status), ten yellow LEDs (stoichiometric), and six green LEDs (rich). The first LED comes on at .05V, the second at .10V and so on, in increments of .05V.

The Air/Fuel Ratio Gauge is wired to an oxygen sensor, a device that measures the presence of oxygen in the exhaust. More oxygen in the exhaust is a result of a lean air fuel mixture and less oxygen is the result of a rich mixture. The "perfect" ratio (not rich or lean) of air and fuel is called the Stoichiometric (STOICH) ratio. Once the STOICH Air/Fuel ratio is achieved, the oxygen sensor will be very sensitive (accurate). Although it can not measure exact richness or leanness, the Air/Fuel Ratio Gauge is an excellent indicator of dangerous conditions. For example, a vacuum leak or a drop in fuel pressure could cause a detrimental lean condition. The Air/Fuel Ratio Gauge will show this condition before damage occurs.

When used in a fuel injected application, the PCM (Powertrain Control Module) uses the oxygen sensor to keep the engine running close to the STOICH ratio. It does this by continually leaning the mixture until the sensor shows lean, then richening the mixture until it shows rich. This continuous loop keeps the air/fuel mixture near the STOICH ratio. Under heavy acceleration the PCM will richen the mixture for optimum power and under deceleration the PCM will lean the mixture for low emissions and economy. The Air/Fuel Ratio Gauge is an excellent choice for monitoring PCM operation.

Although the Air/Fuel Ratio Gauge is a monitoring device, it can be used with a carburetor as a tuning aid. Start with rich jetting, then gradually lean the mixture out until the Air/Fuel Ratio Gauge shows lean, then richen the carburetor back up slightly until there is a rich reading. This should produce the best power, but as always, the final jetting should be verified by inspecting the spark plugs.

For Fittings, The Air/ Fuel Ratio Gauge Kit include non-car-specific instructions but are easy to install, typically just tapping into a +12v power source and the O2 sensor line.