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You have a ground problem either the sensor wire is grounded or the dash isn,t.
Unplug the sensor and see what it does.
Did you get a new sensor for the ford or the dodge.
I hate to say it but even a new sensor can be junk. I would still check for the ground problem first. I once put in 2 O2 sensors before getting a good one.
I noticed another thread where you are having tach problems as well.
With that Cummins installed, are you using Ford sending units or Dodge sending units?
The two may not be compatable if you are using Dodge sending units and Ford gauges.
im using all ford sensors and guages. even the tack its a kit that fordcummins offered the sensor, base and tack ring all it one for the specific year of truck. i dont know if it is a ground issue or not i just put a bigger wire on it and bolted it down in a different location so i will see what happens there when i run her tuesday again
Ground problems, even under the dash are much more common with the newer trucks.
So much plastic in modern dash construction tends to isolate things like gauges from the required ground paths that it is a headache for every manufacturer.
Then on top of that, the bean counters have the engineers use the smallest possible wire size, which after a few years may or may not be able to carry the same load it did when it was new.