What this gauge does is display exactly what your O2 sensor is inputting to the computer. I'm assuming you know how an O2 works. I would strongly recommend that when you install it, hook up a volt meter to watch voltage vs. the gauge. Do a WOT run and see how far into the green the gauge goes. When mine was fuel infected (EFI), it would go 2 bars into the green and DVOM read .7 volts.
You really can't fine tune with this gauge, but it will tell you when you're rich enough at WOT, and will tell you if the engine leans out for any reason. It has helped me immensely a couple times.
Don't buy one that displays a certain air/fuel ratio, like a sweep between 12:1 and 15:1. That is a hoax in my opinion. It's just for a good idea of whether you're close to a good tune, but not necessarily perfect.
Now with EFI, the gauge will switch back and forth as the computer plays with the fuel mixture. Now that I've switched to carb I get a lot better interpretation of what's really going on, and I'll say that the gauge shows a lot richer all the time than with EFI.
A lot of people think it's nothing more than a pretty light show. Those people don't really understand O2 sensors. They're definitely not as accurate as a wide band O2, but common sense should tell you they are pretty accurate. The EPA isn't friendly.
I installed a toggle switch so I can switch between the left and right sensor, also a good idea if you're gonna do this.
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