Why would one install widebands on vehicles that are setup for narrowbands?

Question

A recent post on one of the forums I frequent has piqued my curiosity.

From my limited reading on the topic, widebands do a better job of quantifying air-fuel ratios than their narrowband counterparts, which are sufficient for simple, qualitative rich/lean condition detection.

Some widebands are capable of simulating narrowband output in addition to reporting AFR's, which means that they can replace narrowband sensors.

I have come across a few reasons why one might want to do this, but none of them seem compelling enough to warrant a switch over to widebands:

• More accurate AFR measurements

  For ECU's expecting narrowband output, the fuel management system is already set up to handle qualitative measurements, so I'm skeptical that more accurate AFR's would lead to reduced fuel emissions, crisper engine response, etc.

• Better tuning & diagnostic capability

  I'm not arguing with the benefits of using a wideband here, but I don't expect that tuning or diagnostics will be performed on a daily basis or whenever the engine is running.

So, in short, is there a compelling reason to go with a wideband sensor in a narrowband setup given that all else remains the same on the vehicle?

Answer 1

A narrowband sensor can only measure 14.7:1 AFR (stoichiometric) , where as wideband sensors allows you to measure a range of AFR ~(<10 to ~20). ECU's that rely on narrowband output maintain the AFR at stoich by using closed loop control (cruise etc) and may use various interpolation methods for increasing the open loop accuracy for AFR other than stoich. Depending on the controller algorithm and calibration, it could even give comparable performance to a widband closed loop control.
Using a wideband to simulate narrowband sensor is pretty redundant unless there's some other benefit to be had (lack of availability, cost, future proof)
That being said, a properly calibrated wideband sensor + controller will give you the most accurate AFR measurements across its functional range.
-Running in closed loop allows it to compensate for various environmental changes in real-time and ensure that your car runs within tuning tolerances.
- The car can be tuned more accurately for cruising (slightly leaner than stoich).(marginal mileage gains?)
- More precise tune for wide-open-throttle (performance gain)
However, you will need an ECU capable of running wideband closed loop control. Replacing the ECU may be worth the effort (quite a bit of effort) if you plan on doing further engine modifications.