Why You Need a Wideband O2 Sensor

A wideband O2 sensor is absolutely a prerequisite when adding forced induction to your Miata, regardless of fueling solution. A narrowband O2 sensor, such as the one used on stock Miatas is not adequate. Whether installing a custom FI solution, turnkey "set it and forget it" solution, or something in between, a wideband should always be used. Here's why:

1. Standalone ECUs use widebands to take basic startup maps and help tailor them to your car's specification for basic road tuning. When selecting a wideband, research your selected ECU to verify it can support the wideband of your choice. ECUs with CANBus digital inputs are now common features and highly recommended to ensure your ECU is reading the voltage signal accurately. Note that different Widebands may use different voltage ranges to express a specific Air Fuel Ratio (AFR). 5V is common, but confirm with your ECU/Wideband configuration.

2. Non-adjustable piggybacks (considered bandaids), are outdated tech, but still found in use from time to time. The stock ECU that tells the injector to open and provide fuel under OEM conditions. When the piggyback sees positive pressure, it will intercept the OEM signal and increase it to add more fuel. Non-adjustable piggybacks are one of the oldest and poorest fueling solutions equating to tech from the 1980/1990's, but are frequently found in off the shelf kits (especially kits used for CARB-approval). Because they cannot be adjusted, the manufacturer must often make a solution that fits all Miatas from every climate/environment/model. This means a car could run fine for one customer, but completely rich (or lean!) for another customer in a different environment. In other cases, many non-adjustable piggybacks could be made for specific model/years with different fueling requirements. As they get sold on the secondary market, it may be difficult to tell if it was made for your year. A wideband, even with off-the-shelf kits or non-adjustable piggybacks, will help ensure the right fueling.

3. Other Adjustable fueling solutions (piggybacks, RRFPRs) (still considered bandaids) are the shades of gray in between options 1 and 2. Whether adjustable piggybacks, like the Voodoo, PowerCard, or Rising Rate Fuel Pressure Regulators, the adjustments should be fine tuned. Adjustable solutions may also provide the owner the ability to modify boost settings, and again, the wideband can determine if retuning is needed.

Narrowband O2 Sensors Should Never Be Used for Tuning

A narrowband O2 sensor outputs 14.7:1 as .85-.20 volts. Since the ECU idles at 14.7:1 AFR, it makes small adjustments to ensure the voltage is within that range. Hooked up to a gauge, you will see it sweeping back and forth as those adjustments are being made - bouncing to each voltage and back to the opposite. Since it's such a wide range.

The wideband O2 sensor outputs the O2 readings in the exhaust on a linear scale, so at each voltage increment, it represent a new AFR, when output to a gauge, you can exactly see the correct mixture of O2 mixture in the exhaust.

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