My mileage has dropped 2 mpg on my 09 maxima sv prem.It has almost 49,k on odometer.tires are new DWS Continentals, I always use Synthetic oil at about 3-4k miles and at least the factory or a Bosch filter..?? Why am I only getting 18 mpg for combined driving?? Btw I mainly drive to and from work approx. 14 miles each way..

Did they change your tire pressure. tire pressure affects the mileage dramatically and when ever I have someone change the oil I tell them not to change my tire pressure.

is this calculated mileage or what the estimated mileage is showing on the dash. Have you checked to see what you get on just the freeway?

What are your driving habits like?

How is your tire pressure?

Do you make a lot of short trips?

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An alignment and having the correct tire pressure in good tires ensure better MPG. Economy designed tires help. as they offer less resistance.

You should check to make sure you don't have any parts binding by inspecting each wheel, axle, and the transfer case as well.

Changing from regular motor oil and trans/transfer case fluids to a fully synthetic lubricant will always increase efficiency and performance.

Verify your mileage so that you know what it actually is, by tracking how many miles you are really getting on average per gallon. This takes several weeks to be accurate and it helps to use your trip odometer to track miles between fillups. Maintaining notes about this will help you to know when you need a tune-up, or if something is not working as usual, as you'll notice a change in consumption from your normal average.

Evaluate your own driving habits. Gradual starts, smooth stops, timing the lights so that you don't have to stop, all add up to money in your pocket.

Good luck !

Cause you're driving a bus. lol. Mileage will vary depending on what fuel you use, how you drive, and where you're located. typically what i've seen on trucks like yours, i'm asuming it's a 6.0 liter, is anywhere from 12-19 mpg. you should see around 15mpg for the most part. if you do a lot of in town driving, expect a lot less. @9-12. if it's less than that, i'd start lokking in to it. try running a K&N air filter and use synthetic engine oil. I've seen noticeable improvements with power and mpg's with that. Also, ensure that your tires are properly inflated as that can make a difference in mileage. use the recomended fuel octane and change fuel filters.

anytime a complaint is poor fuel milage and all diagnostics prove to be ok and the 02 sensor(s) have over 70th on them we replace them.

Do not replace the one (s) after the catalytic converter. They have very little to do with fuel control.

Also if you have a MAF in the intake near the air filter these become dirty and sometimes can be cleaned.
When they get dirty the computer will not see the air and in return will not add enough fuel.

is it posible you have a large nail in your tire and the sound is it slapping the road?

Okay... K&N drop-in filter, NGK V-Power plugs (and NGK wires), run tires 2-4psi over manufacturer's recommendation, replace fuel filter anually, use a good fuel system cleaner every oil change, use synthetic oil in the crankcase, transmission AND differentials, drive with windows up and A/C off (just vents), drive 55mph on freeway (this one is HUGE), slow acceleration and try not to drive short distances. These are all "hyper-mileage" techniques that garner better fuel economy. If there is a mechanical problem causing the fuel economy to be bad, the spark plugs, wires and filters ought to be a help.

i hope this helps out,
matthew

Your car should average roughly 32.5 mpg-US (7.24 L/100 km; 39.0 mpg-imp)

The better the engine breaths the better the mileage. Was the new computer a stock computer or performance?

change your spark plugs if they haven't been changed in awhile. check your tires for the propper psi there should be a sticker on the inside of your drivers door that will tell you recomended air pressures go by this not the recomendations on the tires. also where are you getting you gas does it contain ethanol sometimes this can burn faster.