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Narrowband vs. Wideband O2 Sensors

O2 sensors may seem like a very small piece of the fuel tuning puzzle, but they’re really one of the key components to keeping your engine optimized. Using the best equipment is essential for optimizing your vehicle but what’s the best option? How do you make that choice and how do they differ? It’s a little complicated but we’ll explain how O2 sensors work, why they’re so important, and whether you want to keep your stock narrowband or upgrade to a wideband sensor.

The Lingo of Fuel Tuning

When you begin the process of tuning your vehicle, there are some terms that you need to know. These will help you be able to tune more accurately or simply understand what a professional tuner has done for you. These will also help you understand the difference between narrowband and wideband O2 sensors.

Let’s start with the stoichiometric point, or stoich for short. Stoich is the optimal air/fuel ratio that burns both the air and fuel completely in the engine. For pump gas, that ratio is traditionally 14.7:1 but it changes depending on the amount of ethanol present and/or the fuel type used. For other fuel type stoich points we have a table at the bottom to help you out.

14.7:1 refers to the 14.7 parts of air to the 1 part of fuel. So lowering the 14.7 will create a richer air/fuel mixture. 14.7:1 isn’t always the optimal ratio for all drive styles and vehicles either. A racer may use a traditional pump gas but want their ratio to have more fuel added to boost their power output. Tuning helps find the optimal air/fuel ratio for new bike modifications or to simply make more power than stock settings allow.

The ECU uses multiple tables to determine how long to keep the injectors on, which is represented as the injector duty cycle.

Today’s advanced ECU’s don’t just blindly use the tables to determine your air/fuel ratio, they also use oxygen sensor feedback to achieve the target you need.

How O2 Sensors Work: A Science Lesson

O2 sensors are installed in the exhaust and were created to measure oxygen levels within the exhaust. They do this by allowing outside air to come into the sensor that is then heated to charge the ions to create voltage. The difference between the oxygen in the sensor and the oxygen in the exhaust is what determines how much voltage is produced.

That voltage is then sent to the ECU to determine what your current air/fuel ratio is and what needs to be changed to reach stoich. More oxygen means it’s running lean and less oxygen means it’s running rich. What fuel tuners do is offset the ECU signals to change the ratio to make more power or to create adjustments based on new bike modifications.

Narrowband Sensors: The Guessing Game of Fuel Tuning

Narrowband sensors only know three things: lean, rich and stoich. Depending on the oxygen content it reads in the exhaust it sends a signal between 0 and 1 volt. 0 means too lean and 1 means too rich. The ECU, not knowing how far from stoich it is, overcorrects from lean to rich over and over until it eventually gets closer to stoich. The ECU determines where the closed loop is and where the narrowband sensors are active to be able to make these adjustments.

What our tunes do is optimize your air/fuel ratio outside of the closed loop, so even when the narrowbands aren’t active your bike can still be running close to optimal conditions. We also tune the closed loop area to ensure it’s running at stoich, this keeps the bike from needing to ‘learn’ over time to stay tuned accurately.

Narrowbands are excellent when it comes to finding 14.7:1, but they aren’t nearly as accurate when air/fuel reaches either side of this ratio.

Wideband Sensors: Supreme Tuning Capability

Wideband sensors are built for pinpoint accuracy. They send voltage to the ECU on a scale of 1 to 5 so that it knows exactly what is required to maintain target air/fuel ratios. No more guesswork. This also helps your ECU stay more accurate over time with smooth changes instead of the over corrections that narrowband sensors require.

Wideband sensors also open up the entire fuel table to the closed loop. This gives you absolute accuracy of air/fuel ratio at all times, even when you’re pushing your engine to its limits.

This is why nearly all tuning professionals use strictly wideband sensors. It not only gives more control than a narrowband sensor could ever accomplish, but it also gives the tuner a wider range of accurate information under any drive conditions nearly every time.

Stoich Air/Fuel Ratios for Different Fuel Types

Fuel Type Stoich
Pump Gas 14.7:1
E10 14.08:1
E85 9.7:1
Methanol 6.4:1
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