“Sitting for quite some time” seemed to affect both the Explorer and the Expedition….
Which led me to believe that ethanol may have been a contributing factor.
And
You absolutely have to see the downstream and upstream sensors simultaneously and preferably in a “two graph” voltage mode.
Plus: watching both catalyst temperatures comparatively in two graph mode gives you an idea of the performance of one VS the other.
In my case both vehicles had all catalysts within a very close temperature range throughout RPM and driving modes which also prompted me to replace the downstream O2 sensors.
Which led me to believe that ethanol may have been a contributing factor.
And
You absolutely have to see the downstream and upstream sensors simultaneously and preferably in a “two graph” voltage mode.
Plus: watching both catalyst temperatures comparatively in two graph mode gives you an idea of the performance of one VS the other.
In my case both vehicles had all catalysts within a very close temperature range throughout RPM and driving modes which also prompted me to replace the downstream O2 sensors.