All of the engine sensors can affect fuel mileage.
On my 1989 f250 the oxygen sensor is in the exhaust header pipe a few inches in front of the catalytic convertor
Diesels do not use oxygen sensors
The optional diesel engine in an '04 F250 Ford is a 6.0L V-8 Turbo Diesel made by Navistar (International)
it will be on the lower front of the engine even with the crankshaft
Oxygen sensors are pre catalytic converter and post catalytic converter. This means they are somewhere in the exhaust system. Sometimes in the exhaust manifolds or exhaust pipe right off of the engine for the pre cat and in the exhaust pipe immediately after the converter for the post type. Some vehicles have up to 4, yours has 4.
On a 2004 Ford F-250 , 5.4 liter V8 engine : Bank 1 is the passenger side of the engine
In a 2004 Ford F-250 : Gasoline engine choices ( 5.4 liter V8 and 6.8 liter V10 ) Diesel engine ( I believe that is 6.0 liter )
On the exhaust pipe between the engine and the catalytic converter
A 2004 Ford F250 Super Duty Pick Up with 6.0 V8 Diesel engine requires 15.0 quarts of oil.
Which oxygen sensor? There are two of them. They each have 4 wires and each wire has two colors. There were two models of the f250 also, need to know engine size. Sorry.
'03 6.0 takes 15 quarts. '04 should be the same.