Installing an air/fuel gauge

When modifying a turbocharged vehicle (or any vehicle, for that matter) it is very wise to monitor the air/fuel ratio of the engine. Going lean will cause severe engine damage and that has a way of ruining your whole day. Avoiding it is easy, though--just install a Cyberdyne gauge (it is also rebadged and sold under the Intellitronix name brand). The Cyberdyne is available at Summit Racing Equipment for around $30.

Installation is quite easy; there are only three wires to connect. When you install the gauge, be sure to solder the connection to the O2 output signal and also be sure to use a very good source for ground. If you don't do this, the guage will produce an incorrect reading when your headlights are on. (To test your installation, go to WOT with your lights off, let the guage level off, then turn your lights on. Does the reading suddenly drop? If so, one or more of your connections are not good enough. If the reading stays put, you're fine.)

These gauges are a 10-segment LED of various colors; lights 1 and 2 are red, 3 and 4 are yellow, 5 and 6 are green, 7 and 8 are yellow, and 9 and 10 are red. The gauge is actually just a visual monitor of voltage that fluctuates from 0 to 1 volts; each tenth of a volt illuminates one light. Thus a .6 volt signal would illuminate the first 6 lights on the gauge. Once the gauge is in place, you'll see that the light output bobs up and down during normal driving but going to WOT causes the lights to level out at a certain point. This is normal. We are only concerned with how many lights are lit at full throttle.

Now that you have the gauge, you need to learn how to interpret what it tells you. It all comes down to knowing what air/fuel ratio is correct for your particular car and its setup. How many lights should you aim for? Here's how to find out.

Install the gauge while your car is still bone stock. Then install a fresh set of spark plugs, let the engine warm to normal operating temp, and make a few WOT passes where it is safe to do so. Note how many lights illuminate while at full boost. After a cooldown period, park the car and read your spark plugs. Do they say everything is okay? Great. Remember that number of lights and make sure you see them all lit when at WOT.

Later you'll add more power. ANY time you up the boost, do so only 1 pound at a time. After each increase, make a WOT pass through the gears to verify you still have enough fuel. If you now don't light up as many lights, you must add a little fuel to compensate for the added boost pressure. Once your gauge says all is well, make another pass and reread your spark plugs. Do they say you're okay? If so, you're definitely all right.

In summary, that's how you use the gauge. Let it be your guide for each step of dialing in, then confirm your safety by reading your plugs. Once your plugs say that a certain number of lights are safe, always be sure you get that many lights lit and you'll be fine.

Modified 6/24/00.