Air/Fuel Ratio Gauge Installation

An Air/Fuel ratio gauge shows the ratio of air to unburned gas in your exhaust which in turn tells the onboard computer whether your car is running in a rich (too much gas, not enough air) mixture or a lean (too much air, not enough gas) mixture.  Ideally you'd want to be running a stoich (14.7:1 a/f) mixture.  This gauge will bounce back and forth between rich and lean when you are driving normally.  When you hit the gas, it will go into the rich section of the gauge, thus showing that more gas is being injected into the engine under hard acceleration.  This gauge comes in handy if you are running your engine with an adjustable fuel pressure regulator because it allows you to check your air to fuel ratio and eliminate any potential detonation.  Air/Fuel ratio gauges can be picked up at most speed shops or through PartsForYourCar.Com


(this is what the gauge looks like in action)
***** YES, THE GAUGE IS SUPPOSED TO BOUNCE BACK AND FORTH BETWEEN RICH AND LEAN ******

Installation can be quite simple or quite difficult.   The easiest way to install this gauge is to purchase an additional Air/Fuel Pigtail kit from PartsForYourCar.Com


air/fuel pigtail


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The O2 Sensor is located on the back half of the engine block just below the spark plug coils.  It's kind of hard to reach and get at (especially if you have a STB installed).  There is a blue clip that locks the connector together that you need to remove first.  With the clip removed, separate the connector and plug in the pigtail harness.  Replace the one clip and insert a ziptie into the other clip to secure the harness.


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With the pigtail harness in place, crimp a piece of 14 gauge wire to the purple wire on the pigtail and wrap in electrical tape or shrink wrap.  Securely route the sender wire into the passenger compartment through a grommet located to the left of the steering column down by the floor.  Once in the passenger compartment, route the wire up to the Air/Fuel gauge and crimp it to the purple lead using a crimp connector.


(click to enlarge)

If you choose not to purchase the air/fuel pigtail, this install can still be completed.  Granted it will be kind of difficult due to the lack of space and short wires behind the engine.  To tap into the O2 sensor, you need to peel back the black tape covering the wires between the connector and the sensor.  There is a dark purple wire inside this wire bundle that you need to tap into.  Securely tap into this wire and route it into the engine compartment.   Like I said, this can be done, but it's a very tight squeeze. 

All that remains for the install is to supply the gauge with a switched 12volt supply and a solid ground.  I chose to ground mine to a chassis bolt located just inside the fuse box. And the 12 volt switched circuit for my trans temp gauge.


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Fuse Box


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Ground Location

Pictured below is a copy of the wiring diagram for the Autometer Air/Fuel Ratio Gauge:

Questions? Email me & ask