I have noticed that my Scanmaster is showing me the O2 voltages are dropping. At WOT 1/4 mile conditions I used to be around 880mv.

I am now seeing 830-850mv. Is this indicative of something bad.
The performance issue I have is a slight 5500-5700 stumble.

Could the two be related?

 

Could be the A/F ratio is leaner that it used to be. Or it could mean the temperature at which the O2 sensors are operating has changed. That's the problem with trying to tune using stock narrow-band sensors. At 13:1 they are more sensitive to operating temperature than they are to real changes in the A/F ratio.

 

What is each one reading? I noticed simuler changes when I went to race fuel or when the weather changed. Also when my left went bad that was the first thing I noticed was a voltage drop.

 

At the end of a 1/4 mile run they are both in the 840-850 range. They used to be around 880-900.

Does this mean that it has started getting lean or rich?

 

Lean.

 

Or it means the operating temperature of the sensors changed. They are NOT accurate at WOT.