Interpreting O2 Sensor Data - 1999 5.7 Vortec

[kephas]

Hi everyone,

I've noticed over the past year that my Suburban mpg has been worse than before and that it smells "richer" than it did before.

As far as I know, the O2 sensors in my Suburban have never been replaced, so I logged the data on my drive home from work so see if anything stood out.

I put the data in the attached Excel file and made graphs of each sensor. There are some flat line readings in the Pre-Cat sensors. I was watching the data while driving and these always happened under acceleration and deceleration, not at idle. Another thing of note is that the Long-Term Fuel Trims are very inconsistent while driving normally, going from ~-10 to as high as +12-15.

For all you diagnostic junkies out there, does this data suggest that my O2 sensors need to be replaced? Also, please don't comment about deleting the Post-Cat sensors, I'm not going to do that.

Thanks!

 

[GoToGuy]

If the voltage isn't varing constantly adjusting up down, 1, 2, 3 times a second. And you can't remember when, get all 4 and change them. The get old and sluggish, lazy, and the computer depends on them for mixture.
I install new ones every other year, odd years for 95 truck, even for 98 Tahoe. I use NGK/ NTK brand they are quality brand.