One side running richer than the other......

[Bob D]

I checked the condition of my spark plugs and noticed that the left bank is running richer than the right. Is this common ? Maybe I have a bad O2 sensor ? The condition of the plugs on a common side are similar to each other. Any ideas would be appreciated.
Thanks

 

[Bob D]

BigJim, I've never gotten a check engine light. William E-mailed me and thinks it's because of the way the ignition system is set-up. Maybe this is normal. Anybody else notice this?

 

[GTS Dean]

Yes. However, my downstream right sensor seems to require richer long-term adaptive fuel strategy for the right bank. Don't know if this is normal or not.