Just got my wide band installed and I noticed my AFR's bounce between 13.9 and 15.0 during idle with sometimes a little more and sometimes a little less. Is this normal for idle?

 

Yes, normal.

Vehicle is only trying to achive the stoichiometric ratio of the fuel. Basically it swings like it does because thats what the o2 sensors do.

 

Mine is always within 10-20 points and certainly don't see swings like you're describing. You may have an off tune or your wideband sensor may be inaccurate.

 

Isn't a pioint .1? So wouldn't 20 points be from like 13.0-15.0?

 

I should have been more clear, 1 pt = 1/100th. so .1-.2 variation

 

If your running closed loop that is notmal.

 

I figured its in closed loop at idle. Not really sure though.

 

This can be adjusted in your tune in the proportional fueling tables. The idea is this: in order to get your fueling to average out around the stoichiometric ratio of the fuel you're running, it needs some constant alternating proportional error. In control system theory, this is referred to as "set point overshoot". By artificially creating a proportional error and injecting an excessive fuel mass sufficient to overshoot (reduce AFR numerically) your stoichiometric set point (14.68 for gasoline), it reaches the set point sooner. Once the set point has been overshot, the opposite occurs: injected fuel mass is reduced excessively to once again reach and overshoot the set point in the negative direction (increase AFR numerically). There is a way to calibrate this precisely, and in the case of OE vehicles it is further complicated by catalyst specifications, as proportional fueling is what is used to manage oxygen storage in a catalytic converter. However in the aftermarket, 999 out of every 1000 tuners will simply adjust the proportional fueling tables until it 'looks good'...I'm no exception here, as I do the same thing. The changes to proportional fueling generally need to be made when swapping in a different camshaft. I tend to see larger NA cams need more closed loop proportional fueling, whereas bigger PD supercharger cams often need less proportional fueling. If your O2 voltages appear to be lazily switching, taking their time, you need more proportional fueling. If your O2 voltages switch and hang rich/lean for too long, you need less proportional fueling. I'd say in your case since it looks like you're concerned about the latter, you may need less. However unless you're getting torque surge from the proportional fueling being off, I wouldn't be too concerned about it.

Hopefully this addresses your concerns..

 

Good info! Thanks jake.

 

My gauge can display o2 b1s1 mv. Is this the same thing as o2 output voltage?