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The monitor receives the oxygen sensor signal output and turns on light emitting diodes (LED) to indicate the air/fuel ratio of the engine. If the air/fuel ratio is very lean, the red LED’s will be on. When the air/fuel ratio is in the safe but lean condition, both the red and green LED’s will be illuminated. As the air/fuel ratio gets near optimum or stoichiometry, only the green LED is on. As the air/fuel ratio goes richer still, both the yellow and green LED’s will be on. When only the yellow LED is displayed, this a very rich air/fuel condition. The air/fuel ratio range for the green LED (all three conditions) is very narrow. The range from the red and green LED’s illuminated to yellow and green LED’s illuminated is +/- 0.15 air/fuel ratio. The range for the green only LED is +/-0.05 air/fuel ratio. During warm-up of the oxygen sensor, the signal from the sensor is low in strength. During this time the monitor will have the yellow LED on. As the sensor warms up due to the engine operating, the yellow LED will go out unless the engine is truly rich. If the sensor wire is open (disconnected), the same condition will appear.

The driver’s favorite feature of the C&S Air/Fuel Ratio Monitor is the telltale/latching capability. The telltale/latching feature allows the driver to lock-in a reading at any place on the track, without looking at the LED display, by simply pushing a button. The air/fuel ratio reading at that instant will stay latched in memory until the button is pushed again which unlatches the display. This allows a reading to be retained for the crew chief in the pits. When the latch switch contact is closed, the data is locked on the display and an orange LED is illuminated. Opening the contact will return the display to normal, real time mode and the orange LED will extinguish. This is important in racecars to latch information when the driver’s attention needs to be on driving rather than data retrieval. It is also helpful on “catching” a transient operating condition such as heavy acceleration, braking or cornering.

Although the C&S Rich-Lean Indicator (Air/Fuel Monitor) contains a small computer, NO computer knowledge is required to install or use. It represents the latest technology and is rugged enough for dirt track cars but as easy to install as any other gauge. A tech brochure is included. And, as always, C&S' Tech Hotline is available from 7:00 a.m. til 5:00 p.m. Monday through Friday at (636) 723-4996.