What is a Wideband O2 gauge and why do you need one?


We get a lot of questions in the group about carburetor adjustments.  From headers glowing to rough idle, stumbles, and lack of power.  Sometimes it can all seem quite confusing.  While you can read your plugs to tell how your engine is running, it doesn't tell the whole story.

A wideband afr sensor is commonly used in vehicles equipped with computer controlled efi. But this little device can prove itself priceless when you are trying to tune your carburetor equipped vehicle.

Imagine knowing EXACTLY what is going on inside of your cylinders.  When you feel that stumble, look at your gauge.  Is it rich, is it lean, well now you know and you can now diagnose what is causing this condition.

There are 2 types of sensor/gauges.

A narrow band o2 sensor is an oxygen sensor that is only calibrated to know three things. Rich, stoic, and lean. What I mean by this is that it only has a narrow window that it see’s the air fuel mixture through. The sensor can tell the gauge when it’s stoic. If it’s not stoic, it can tell the gauge that it’s either Rich, or Lean, but that’s it. It doesn’t really output any particular value other than that. How rich the engine is the sensor has NO IDEA about. Same with how lean the engine is. All it does know is that it’s not stoic. While these units are much cheaper, we do not recommend wasting your money on them.

A wideband o2 sensor is much more sophisticated than a narrowband sensor, and can be relied upon to be used as a tuning tool.  Wideband sensors not only are a lot faster acting in the reading, but can tell you the exact a/f ratio that the motor is currently at. So instead of just telling the gauge that the engine is running rich, it will read a voltage that correlates to an actual value, like 11.2. One thing to remember with a wideband sensor is that it has a heating element that needs to be heated up before the sensor will be accurate in its readings. This usually only takes a few seconds, but just remember that for those first few seconds the gauge is not useful.

We installed the AEM 30-4110 in the work truck and it has performed flawlessly.  Since changing engines, we noticed that our 350hp rated engine seemed sluggish. The afr gauge shows that we were a bit rich on the main jets but yet the plugs looked good. We took the mains down 2 sizes and the engine woke up. There is still a bit of tuning to be done but the wideband at least tells us in which direction to go.  These units run about $150 on FleaBay.

What is Stoic, Rich, and Lean?

Stoic, rich, and lean are terms that we use to describe the burn ratio of fuel to air in the combustion chamber. The perfect ratio for good combustion of every fuel is called stoic. A stoic value will always give the motor a good clean burn while taking gas mileage into account as well. However, stoic is not a good number to shoot for in a performance engine that is under high load.

Rich refers to conditions in the air fuel value were there is more fuel present than is ideal to the air content. Rich conditions will cause the burn to use more fuel, but can also offer more power at the same time.

Lean refers to conditions in the air fuel value were there is more air than fuel. This causes the combustion to occur rapidly and burn very hot. Think of a cutting torch when you add more oxygen. While this is great for gas mileage while your cruising down the highway, under hard acceleration the super hot flame becomes dangerous to the motors internals (pistons, and valves)

What do all the numbers mean?

AFR Values & Characteristics 

6.0 AFR - Rich Burn Limit (engine fully warm)
9.0 AFR - Black Smoke / Low Power
11.5 AFR - Best Rich Torque at Wide Open Throttle
12.2 AFR - Safe Best Power at Wide Open Throttle
13.3 AFR - Lean Best Torque
14.6 AFR - Stoichiometric AFR (Stoich)
15.5 AFR - Lean Cruise
16.5 AFR - Usual Best Economy
18.0 AFR - Carbureted Lean Burn Limit
22.0+ AFR - EEC / EFI Lean Burn Limit

Lean Conditions - Common Side Affects
Hotter Engine Temperatures
Detonation / Pinging
Hesitation in Throttle Response

Rich Conditions - Common Side Affects
Engine Flooding
Decel Pop / Backfiring
Lethargic Throttle Response
Excess Carbon Build-up (sooty pipes)
Fuel Smell from the Exhaust

Installation is very easy and pretty straight forward. Our unit came complete with the weld in bung and detailed instructions on how to hook up the 3 wires, yes it's that simple.

So would we recommend installing one in your vehicle?... ABSOLUTELY!!!

You'll be wondering why you didn't do it sooner.