Hello! I bought my 97 Max last year at the beginning of the winter. I kept all the gas receipts and I'm getting 14-15 mpg all the time. Based on 50/50 city and highway. Since the high gas price these days, I deceided to tune my car a little bit. I changed my spark plugs to NGK Iridium IX and a new fuel filter. Air filter seems fine and I didn't change. Last night I filled up the car and I got 220 miles out of 15 gallons. So do I need a major tune up or will it get better with the weather getting warmer? Any suggestions are welcome. Thanks. =)

 

I would check to see if your knock sensor is tripped. It won't generate a CEL, so if it's gone bad or a knock has been detected, you won't know unless you check it yourself. If it has been tripped, your ECU will retard your timing and mess up your mpg. Also, I would do an induction service. A lot of people will say it's bullcrap, but I know it helped me slightly raise my mpg when I did it (5-10 miles/tank). Plus, I hope you're using 93 octane gas and not that cheap crap. Hope that helps.

 

Change your O2's as well. They control the a/f ratio and as they age they become less accurate.

 

http://forums.maxima.org/showthread.php?t=517994

 

i know weather/temperature would play a pretty big role. in my old infiniti J30t in the winter i'd get about 6.5-7.5km/L(15-17mpg) and in the summer doing the same route, with the same harsh driving style i got about 8km/L( about 18/19mpg). changing the octane didnt make any significant gas mileage differences for me, but the O2 sensors made a huge diff, as when i first got the car i was only getting about 6km/L in the summer.
Hope this helps

 

A bad MAF sensor can do this as well. Check your tail pipe to see if their is a lot of black crud on it. If so it means your running rich and it is becasue of one of the sensors.