01 expedition fuel mileage

This can only be a guess since I don't have the mileage. Around a 100k on the odometer and fuel filter never changed..
No filter then the screen on the fuel pump inside the tank.

how old is and mileage.

try changing fuel filter and making sure tire pressure is correct keep your car clean so air can flow freely and try an oil change all these factor into good gas mileage and you could try adding new plug wires to your tune up

Check your air filter,probably needs changing.Replace spark plugs.

You can change the spark plugs and coils, wires for a little better gas mileage. I would say 60,000-70,000 miles. If you are under that, probably still ok. You can try fuel injector cleaner in the tank. Check your tires and make sure they are properly filled up. If the vehicle is out of alignment, it will cause bad gas mileage. Make sure you have no vacuum leaks and make sure your air filter is clear. If you have any questions, just let me know.

try pouring a can of seafoam in your fuel tank,,this will clean the entire fuel system and will improve HP and fuel economy.

The 02 sensor near the firewall would help. Change your plugs, fuel filter, and air filter.

there are lots of things that can affect gas mileage. if the spark plugs and wires are worn out, the air filter being dirty, dirty fuel filter, proper inflation of the tires, O2 sensors that are contaminated and performing poorly. the first thing to do would be that the engine is in good working order, as in no check engine light, no misfire, etc. a poorly running engine will put out terrible gas mileage. then you can start with the things i listed.

Usually when it comes to bad gas mileage, an air filter change, fresh oil and filter, fuel filter and making sure you have no vacuum leaks....

Also, believe it or not, improper tire pressure will affect your gas mileage.

New spark plugs and wires are a "nicety" but if there is not damage to them, then they will be fine.

The PCV and the fuel filter replacements are not going to increase you fuel mileage. What you should really consider is getting some good fuel injection cleaner into the tank, and get an "induction system cleaning". Those two items alone will address most of your mileage issues. The PCV does nothing for mileage, nor does the fuel filter. Also, for maximum fuel mileage, you should have the correct sparkplugs from Toyota in your car. "Aftermarket" plugs doe not perform very well at all.