2004 Tribute. Fluctuating Gas Mileage
 

I have a 2005 Mazda Tribute 3.0 with 162000 miles. It runs great. The problem I'm having is that I get different miles per gallon for every tank full. On one tank full I will get 19 MPG, then the next I will get 15 MPG, then 13 MPG, Then 10 MPG, then 15 MPG, Then 19 MPG, and so on. Originally I used to get 20 miles per gallon.

I have replaced the spark plugs, spark plug wires/coils, and every filter I can think of. I’m the type of driver that does not have a heavy foot.

What is weird about this issue is that the gas mileage fluctuates so much.

Can anyone tell me what could cause this?