Car getting 16mpg combined, help!
 

It's my fathers car, he drives it normally.

It's got like 110,000 miles on it.

What could be making it so inefficient?

I think someone mentioned we should clean the MAF, TB, IACV, and EGR. Is that true? How can we tell if those things need to be cleaned? And how much will it improve efficiency?

Also, does not having the tires balanced and the wheels aligned properly also affect fuel efficiency by so much?

Well, im blessed if i can pull of 16mpg in NYC.

but, start with changing the spark plugs, fuel filter, air filter, and clean the maf, tb, iacv,and egr and go from there.

any Check engine light on?...Maf, air filter, spark plugs, bad O2 sensor, low tire pressure all can cause low mpg...do you smell gas?

Hmm... he drives mostly in the city, so I guess that contributes to it. His air filter is ancient... he thinks just shaking the dirt out of it is sufficient. I will buy a new one.

Yellow check engine light is OFF. I read the codes from it and only the knock sensor code shows up.

There is no gas smell.

only his left front tire is balanced, all the others are not. Plus I think the front wheels are not aligned well. Would these things make a big difference?

There's your MPG killer.

Really? How does it make the car so inefficient?

Take a read.

http://forums.maxima.org/4th-generat...operation.html

start with the air filter... i have knock sensor code,wheel pulls a Lil to left so need alignment and i drive it hard and get a Lil over 25 hwy and 20-22 city... air filter is a biggie on mpg so are plugs

Cheap gas or good stuff?

Wow man, thanks for that link!

I drove his car years ago and it rolled freely and easily, drove it again recently and I had to add a lot more gas. I guess that could be the knock sensor... gonna go and replace it!

i use 93 octane at BP most of the time and i drive alot of city since my school is 70 percent city 30 percent highway and i get 17 mpg but i like shifting at higher rpms at times but when i shift at 2500 it gets pretty good

Also, my dad uses tap water for his engine coolant. He has been doing this for a year or more because the radiator was leaking. He put in a new one, but still has tap water in it.

Is that bad?

Should he put in antifreeze?

tap water= calcification.

Not necessarily, but it does affect it. I can slam 22-24 city all day and my knock sensor has a fat crack in it. (Yes it's in my to do list lol)

Op: for what it's worth, I used to have a ~16 mile commute to work everyday. And I averaged the mpg mentioned above. HOWEVER, I have recently relocated job sites, and it's now only 3 miles one way. I now only have to fill up every two months, instead of every week, but I have noticed my overall mpg has dropped to about ~18 mpg.

TL; DR: shorter commutes = less mpg

Wow, i'm in for solutions as well. My car has 16 city as well. And if i do 100% highway, i get around 19 mpg. I changed both my primary o2 sensors with this :

http://www.ebay.com/itm/360566119084...84.m1439.l2649

That didn't solve my problem. If i'm correct, only the primary sensors calculate the air/fuel right?

I have no codes at all except the P0138 every few months. (It pops up maybe once every 3-4 months maybe?) With an addition to P0158. But those two codes haven't popped up yet since i changed my o2 sensors 3 weeks ago.

Will cleaning the maf, and throttle body actually increase mpg alot? I plan on doing those things when i convert to cold air intake.

The 4th Gen Maxima MPG ratings were 19 city 25 highway. Obviously, with heavy driving, that'll go down. Shorter trips, that'll go down. Vehicle not up to maintenance, it'll go down.