Dawes Devices
Gen II Air/Fuel Meter Instructions



Congratulations on your purchase of a Gen II air/fuel meter. Improvements over the previous model include improved signal dampening and filtering. We now have the brightest, display of any A/F meter available. No other air/fuel meter is easier to read under race conditions.

Our meters contain no wearable parts and should provide years of service if you follow the following precautions; Do not attempt to open the meter as it has been sealed shut to increase the strength of the case. If you need to clean the meter, use a soft cloth moistened with window cleaner or rubbing alcohol. Do not expose the meter to water.


The meter may be mounted anywhere inside the vehicle using velcro or double sided tape. The meter may be pointed at the windshield to achieve a reflection, for a “heads up” display. Under the top edge of the dash, or on the fixed portion of the steering column are also good choices. Try to place the display in your line of sight, so you can keep your eyes on the road when it’s most important. When running the wires through the firewall, be careful to avoid contact that could wear the insulation on the wires. One of the existing wiring harness holes, with its grommet, should work well. We suggest mounting your meter with a piece of tape, until you determine the location that suits you best.
The In-Dash version of our meter allows for custom installation of the display lights. Each light includes a bezel that may be mounted in a 1/4″ hole. After popping each bezel into a hole, the corresponding light may be pushed in from the rear. Each light will snap in place, inside each bezel. The display lights may be pointed at the windshield to achieve a reflection, for a “heads up” display. The meter electronics package may be mounted anywhere inside the vehicle using velcro or double sided tape. Try to place the display in your line of sight, so you can keep your eyes on the road when it’s most important. When running the wires through the firewall, be careful to avoid contact that could wear the insulation on the wires. One of the existing wiring harness holes, with its grommet, should work well. We suggest mounting your meter with a piece of tape, until you determine the location that suits you best.
The meter requires three connections to operate. They are:

Red Wire,12v supply-Connect this to a switched 12v source. You can also connect this to the battery, as the display is disabled when the engine is off. Use a 2A fuse if you connect directly to the battery.

Black Wire, ground-Connect this wire to the negative post of the battery. Do not connect the ground wire to the body, or anywhere inside the car. You will get false readings indicating a lean mixture when the mixture is actually much richer. Because all air/fuel meters read voltage between ground and the O2 sensor, the ground is very important. E-mail info@3barracing.com, if you have any questions.

White Wire, sensor signal—Connect this wire to the oxygen sensor signal wire. Consult your wiring diagram, but the black wire is usually the signal wire. Note: Use REAR O2 sensor output for Subaru WRX installations.
On three-wire sensors, the white wires are for the oxygen sensor heater. The black is the signal.

On four-wire sensors, the gray is the ground and the black is the signal wire.

You can increase the accuracy of this meter by equipping your vehicle with a 4-wire sensor and connecting the meter ground wire directly to the oxygen sensor. Try one from a 91 Shadow.

It is recommended that you solder the connection to the O2 sensor and all wire extensions, rather than use crimp type connectors, which may result in a poor connection. If you do not have the means to solder the connections, seek a car audio shop to assist you. The connections to the battery do not need to be soldered.
The meter will begin to give useful readings once the oxygen sensor has reached operating temperature-about 5 min. At idle, or under cruising conditions, it is normal for the display lights to flash as the computer adjusts the mixture. The readings will stabilize under wide-open-throttle conditions, when the computer reverts to a programmed fuel map. Air/fuel meters can only be used under wide-open- throttle conditions. Under these conditions, you will notice that one light on the meter is illuminated. By keeping the readings out of the red, you will enjoy good power and reduce the risk of damage from a lean mixture.

This meter is calibrated in .04v increments, with the yellow light showing the minimum safe zone. You may run richer if you choose, for an added margin of safety. Please note that your meter comes with the following range:

1st light (red)=.78v-.90v — If the red light stays on for more than 1 sec during WOT acceleration, or no lights illuminate within 1 sec, you do not have a safe amount of fuel to support your boost level. It is suggested that you remedy the situation immediately.

2nd light (yellow)= .90v-.94v –Ideal for most racers, a safe amount of fuel is present for your boost level.

3rd light (1st High Intensity Green)= .94v-.98v-A little rich, you have enough fuel to support more boost. You may choose to run like this, and enjoy the extra measure of safety, but you will gain power with more boost or less fuel.

4th light (2nd High Intensity Blue)= .98v to limit of O2 sensor-Too rich for good power. Reduce your fuel delivery, or raise the boost

As engine speed increases, it is normal for the readings to decrease. As long as the yellow or green light stays on, you are getting sufficient fuel.

It is possible to illuminate two lights at once if the meter is between ranges. This is normal, and actually shows you very precise information.

Note: If you do not have a 4-wire sensor, you can improve the readings by upgrading your O2 sensor. Request an O2 sensor from a 92 Shadow from your parts store. The extra ground on this sensor can be joined with the meter’s ground wire and connected to the battery. The resulting output will be slightly higher and may inform you that you have even more fuel available than you thought.
Most problems are caused by incorrect wiring. Although the meter is protected from incorrect polarities, if will not function correctly if mis-wired. Use the following steps to help you troubleshoot your problem. Be sure to let the vehicle warm up. The sensor is not active for the first few minutes before it gets hot. Also, the meter will only operate momentarily under cruise and part throttle conditions. It is designed to be read under full throttle acceleration.

-No lights: Check all connections. It is possible that you have the white wire connected to the ground wire of the oxygen sensor. Removing the white wire from the sensor and momentarily touching it to a 12v source will verify meter operation. The last light should come on.

-Blue light stays on all the time: You have the white wire connected to 12v. You may have connected to the 12v line for the oxygen sensor’s heater.

-Lower than expected readings: Solder your connections to the oxygen sensor. You may also have a weak sensor, or your engine is running leaner than you thought.

Note: This product is intended to monitor the relative air/fuel ratio, as measured by the oxygen sensor. Dawes Devices will not be held responsible for damage resulting from the mis-use of this product.


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