O2 ?

[Jeff Niceswanger]

Originally Posted by Jeff Stout

If a O2 sensor is going bad what will it do? Mine is showing 18 to 21 AFR now and car is fine and runs the same. Last month it was showing 16 to 18 AFR. No header gasket leak that I can hear or see. Plugs read normal and ET is where it should be. The sensor is about 3 years old with C12 and C16 for fuel

Jeff
If your 02 goes bad and you see little to no changes,you are most likely on open loop and the 02 has no effect, other than taking readings. Your unit is just following the map, period.(By readings I mean your data recorder in your FI unit, or stand alone unit.) You could also have a well tuned map using closed loop, and whoever did it has the allowable corrections so slim that even if the FI units sees a lean condition, its only making minimal allowable changes. Those 02's always fail in a lean condition, so if the parameters are set high (20-100 %) your FI unit will recognize the false lean condition from the failed 02 and dump whatever is available into the motor trying to correct the issue. That's why most tuners set that value pretty low after finishing up a tune. Just in case of a 02 failure. But I'm guessing your in open loop,,,,,
Hope this don't make it worse, ......LOL

[cmracing]

Originally Posted by Jeff Niceswanger

Jeff
If your 02 goes bad and you see little to no changes,you are most likely on open loop and the 02 has no effect, other than taking readings. Your unit is just following the map, period.(By readings I mean your data recorder in your FI unit, or stand alone unit.) You could also have a well tuned map using closed loop, and whoever did it has the allowable corrections so slim that even if the FI units sees a lean condition, its only making minimal allowable changes. Those 02's always fail in a lean condition, so if the parameters are set high (20-100 %) your FI unit will recognize the false lean condition from the failed 02 and dump whatever is available into the motor trying to correct the issue. That's why most tuners set that value pretty low after finishing up a tune. Just in case of a 02 failure. But I'm guessing your in open loop,,,,,
Hope this don't make it worse, ......LOL

This is how I tune engines. Get them right, then lower the correction limits so in case something goofy happens, you don't hurt your engine.

Yes, they tend to start reading lean when they start to fail. The typical low-dollar sensor usually lasts 75-100 passes, a lot depends on your tune and how you run the engine. Lots of cold starts and running rich shortens their lifespan.

Keep a spare on hand. I used to buy the good NTK sensors for my Holley setup, but the Bosch sensor which lasts about 1/2 the amount of time is also 1/2 the cost, so it's a wash........

I really only use the wideband to log things, I usually run stuff in Open Loop unless a big change has been made or a much different altitude track is going to be raced at. Even then, 5% correction is typically enough.