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K&N Air/Fuel Ratio Monitors

K&N Air/Fuel Ratio Monitors
A K&N Air/Fuel Monitor is a precision instrument which has been created to assist performance enthusiasts calculates an optimum air/fuel mixture ratio. It works on carbureted, injected, supercharged, or turbocharged engines using unleaded gasoline, alcohol, propane or nitrous oxide. It does not work with nitromethane or diesel fuels. The monitor comes with a tuner to adjust for power, economy and/or improved drivability.

To "read" the air/fuel mixture, the system uses an oxygen sensor to sample the exhaust gas.  The sensor "sniffs" the exhaust and measures the amount of oxygen present in the spent gases.  When used as part of a computer controlled feed-back system, the oxygen sensor tells the computer (via a small electric signal) when the air/fuel ratio is rich, lean or just right.  The computer reacts to the signal by re-calibrating the fuel delivery system thousands of times per second.  This feedback control loop, or "closed loop" system maintains a near perfect air/fuel ratio throughout the entire operating rpm range.  Your K&N Air/Fuel Monitor uses this same electric signal to illuminate a group of 10 LED lights that correspond with an air/fuel ratio scale. Reading the scale will tell if your fuel calibration is rich, lean or just right.  Using the Monitor as a tool, a tuner can adjust for peak performance, economy and/or drivability under any load condition or throttle setting.

  Light 1 Light 2 Light 3 Light 4 Light 5 Light 6 Light 7 Light 8 Light 9 Light 10
Gasoline 17.1 17.1 16.0 15.1 14.7 14.7 14.7 14.7 14.0 13.2 12.1
Alcohol 7.6 7.6 7.1 6.7 6.5 6.5 6.5 6.5 6.1 5.8 5.3
Propane 17.9 17.9 16.8 15.9 15.6 15.6 15.6 15.6 15.0 14.0 13.0

A K&N Air/Fuel Monitor has many uses. For example, it can be used as a guideline for preparing a vehicle for emissions testing or as a piece of dynamometer test equipment. Or calculate the amount of carbon monoxide (CO) and hydrocarbon (HC) emissions as related to the air/fuel ratio. Leaning the air/fuel mixture reduces CO and HC emissions. The Air/Fuel Monitor can also be a helpful tool when setting the idle mixture screws on an engine equipped with a large camshaft and automatic transmission. Chock the wheels, start the engine and put the transmission in drive. Adjust the idle mixture screws until the 8th light on the Monitor glows steady. The engine should then idle in drive without stalling. 
Installing an oxygen sensor in each exhaust pipe is an excellent way to confirm a fuel distribution problem. If you would like to monitor both banks, install a second oxygen sensor in the other pipe. Then switch between the sensors with a switch (purchased locally).


The oxygen sensor in your K&N Air/Fuel Monitor assembly is not compatible with leaded fuels or any fuel additive containing lead. Leaded fuel will contaminate the oxygen sensor causing it to deliver a false reading. The Monitor can, however, be used to momentarily test an engine burning leaded fuel. Simply install the sensor - re-calibrate the fuel delivery system to deliver the desired air/fuel ratio - then remove the sensor to avoid prolonged exposure. This short term exposure will extend the useful life of the sensor when testing an engine burning leaded fuel, but eventually it will become contaminated. Once contaminated, the sensor must be replaced to restore the accuracy of your instrument. Additionally, since there is no efficient way to test the sensor, there is no way to determine the level of contamination. Therefore, we recommend periodically comparing a used sensor to a new one.
Other products that will contaminate or clog the sensor are: 
• Gas/oil mixture • Injector or carburetor cleaners contain lead additives 
• Octane boosters containing lead • Other "secret potions".

Round "In-dash" Complete Kit (includes monitor, sensor and weld-on fittings)  85-2441

Rectangle Monitor only   85-2439

Oxygen sensor only (includes weld-on fittings)   85-2438

Weld-on fitting   85-21688

O2 sensor plug   85-21686

Under-dash mount gauge bezel, for round monitor, black finish   85-2443

O2 sensor bushing and plug   85-2440
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