Im getting 350 Kms per full tank in my maxima , alot of my matinence is up to date . Fuel filter was changed a year ago , air filter is still good , sea foamed the car twice in the year , o2 sensor was changed I have 15 stocks on , not alot of weight either. My allignment is a bit off though , so im considering getting an allignment done but one of the techs at a garage said its pointless to get it done ....

 

To calculate MPG, fill up, reset odo, drive until near empty, fill up again, same pump if possible, read miles driven.

Now divide miles driven by number of gallons used.
Report results.

Basing your fuel consumption from your fuel gauge isn't accurate at all.

Make sure your tire pressure is correct, it should be checked cold.
The alignment will help by reducing drag.
What type of driving do you do from day to day, city, highway or a combo of both?