Hi, I’m Jay from Real Street Performance. Today we’re going to talk about how to use your wideband air/fuel ratio gauge and interpret the data that it’s telling you. For sake of discussion and trying to get you guys to understand this concept, we’re talking about stoich. Your target air/fuel ratios will often be different than stoich. A wideband O2 sensor has a 0 to 5 volt range, and it will output a signal from a 10 air/fuel ratio to a 19.0 air/fuel ratio and everything in between with pinpoint accuracy. A narrowband O2 sensor has a 0 to 1 volt output. And it will just read above or below stoich. So it’s used for factory systems to control closed-loop fueling under low load for good gas mileage, but it does not output a signal that you can identify as an air/fuel ratio. Since a narrowband sensor can output an actual air/fuel ratio, we just don’t use them for tuning. The exhaust gas leaving the engine is a mixture of air and fuel. If there’s too much air present the mixture is lean, and has too much fuel present the mixture is rich. If exactly enough air is provided to completely burn that amount of fuel, it’s called the stoichiometric ratio. Different fuels have different stoichiometric values. Some require more air than others to create a stoich mixture. For reference, pump gasoline has a stoich ratio of 14.7:1. So that’s 14.7 parts air to 1 part fuel to create a stoichiometric mixture. This is why most of the commercially available wideband O2 sensor gauges on the market are 14.7 when you click them on cuz that’s the stoich ratio for pump gas. This is why most of the aftermarket wide bands are set up with a 14.7 stoich ratio because they’re assuming that you’re running on pump gasoline. When you’re using your wideband air/fuel ratio gauge as a tuning tool, you have a target that you’re trying to reach. So you’re going to adjust your fuel map to reach that target. But we know that the air/fuel ratio is different for each fuel because the stoich ratio is different. Since different fuels have a different target air/fuel ratio for stoich, if you drain the gasoline out of your car and put ethanol or E85 in it, would you target a 9.7 air/fuel ratio on E85 on the same gauge that was 14.7 on gasoline? You would have been making a mistake if you had done this because the sensor itself just knows that stoich is stoich and the gauge is configured on a gasoline scale. So even though E85 has a stoich ratio of around 9.7, the display on the gauge would still be targeting or you would still be targeting a 14.7 ratio. Don’t worry if you’re getting confused. Everyone else is too. There’s a much easier way to do this and it’s just a work in Lambda. Lambda is the direct output of the sensor that the manufacturers translate to an air/fuel ratio on the gauge. Most wideband manufacturers offer an option to display in Lambda instead of air/fuel ratio. So you can just get used to working in Lambda. The beauty of working in Lambda is regardless of the fuel you’re using, the stoichiometric ratio is always the same. It’s always 1. So if you’re tuning for power under boost, you may target 0.75 to 0.77 Lambda, and that’s just the number that you’re looking for regardless of the fuel that’s in the tank. So in my opinion working Lambda is easier because you don’t have to memorize or have any thought of a conversion between the actual sensor and the display because you’re always just looking for the target Lambda value you’re after. After installing a wideband there are some people that overreact because they don’t know how to interpret what the wideband is telling them. It’s normal for the gauge to display lean during deceleration. The ECU generally cuts fuel while you’re slowing down because the engine doesn’t need fuel injected in it to slow down. During part bottle cruise, it’s normal to see ratios if you’re working the Lambda of 0.95 to 1.05 or air/fuel ratios of 14.0 to say 15.5. Totally normal. It’s normal to see on a naturally aspirated engine under high load or wide-open throttle a Lambda value of 0.85 to 0.91 which is going to be 12.5 to say 13.3 if you’re still working in an air/fuel ratio. If you have a forced inducted or a boosted engine, you’re generally going to see 0.75 to 0.80 in Lambda or 11.0 to 12.0 air/fuel ratio under high load. The sensor relies on an internal temperature for its calibration to be correct. That’s why it has a heater circuit. If you first start the car up, the display may not read correct until it reaches its operating temperature. If the sensor becomes fouled or damaged or just wears out, it’ll typically read lean under no load or loaded conditions where it’ll just go to the top of the range and just sit there. That’s when you know it’s time to buy another sensor. Hopefully this information helps you understand what your wideband gauge is trying to tell you. And you can see what’s ordinary and what’s out of the ordinary. If you have any questions, you can consult the guy that tuned your car or give us a call or post questions in the comments below. Thanks. and I’ll see you next week.