Fuel mileage has gone from 14 to about 8 mpg. put fresh air filter in and no help..engine is 5.8 fuel injected 54,000 miles auto 4x4 reg cab. thanks ed.

 

Way too many variables. Unless someone who has experienced the EXACT same thing posts about something specific to look for, you gotta start from the top.

Any mods made that could have caused it?
You change fuel?
How's your tire pressure?
What's the weather been like?
Check all driveline systems for worn bearings, draggin' brakes etc.
What kind of transmission?

 

no dragging brakes . tires are fine. no mods . transmission automatic with overdrive. what about tps sensor or mass air flow meter?

 

Does it run OK?

When were the sparkplugs last changed? Fuel filter changed? Have you run some injector cleaner through it to get everything "squirting" good?

 

runs fine. spark plugs changed , fuel filter changed. just uses allot more fuel . 8 mpg the best .. regualar size tires..just a bone stock truck.

 

Has the mileage been bad for several tanks or just the last one or two? You might try a different filling station like monsta suggested. You also might try resetting the ECU by disconnecting the battery for half an hour or so.

Have you checked & re-checked the plugs and wires to make sure they are all OK?

 

mileage has been bad for about 10 tank fulls. tried diffrent fueling stations no luck ..will try the ecu disconect thanks..spark plugs are fine.

 

Has performance decreased at all along with the fuel mileage decrease? What does the end of the tailpipe look like? Full of soot? (not diesel soot )
Is your gas tank leaking?
It gotta be running real rich to lose that much mileage or something is "draggin'" (you'd notice but we talked about that before.) or the transmission is suckin' up a lot of the power somehow.

The sensors you mentioned, if bad, would throw a light. You'd also notice a decrease is performance somewhere.

 

no . no soot. gas tank is not leaking .no loss of performance that i can tell of. no dash light thrown. but thanks for the sugestions ,. if you can think of anything else keep them coming thanks ed.

 

I hate to see someone throw parts at a problem finding a cure.

With that said,oxyxen sensors do take a beating and can be one of the first sensors in the fuel injection system to fail.You will not always get a Check engine light or fault code when one starts to fail.