My car the past month has been averaging between 14 to 18 mpg with mixed driving. I know its cold out but it was NEVER this low. I have had a full tuneup on the car at 120k miles, new air filter a month a go, just had an oil change, and tire pressure are 33psi cold all around. I have no check engine light on, last thing I did was change the EGR solenoid valve. My fuel injectors were replaced 20k ago and the car drives fine. I am not driving aggresively either so I cant explain why its running rich. I also did clean the throtle body 20k ago, new knock sensor and I use 93 rated gas.

I am calculating the gas mileage the right way, dividing the number of miles by the amount put in. I thought maybe on the highway it would give better but it only gave 18mpg, this is with 70 percent high way driving. 293 miles on 16.5 gallons. Any one know what to look for? The car has 150k miles, the auto tranny was flushed out 10k miles ago.

 

that's normal...I get around 16.4 mpg all around. remember we all have v-6, not some weak 4 cylinders.

 

Yes but a month or two ago I use to get 21 to 22 mpg when doing mostly highway. The weather was pretty much the same.

 

That's winter gas for you man. Im getting the same gas milage as you, and nothing is wrong with my car that I am aware of.

 

16mpg is pretty low. My Q45 gets roughly 15-16mpg, and thats a 4.1L ....

 

My guess is its the winter mix gas, especially if you have taken all the steps to correct it. I really thought i would be getting better mileage out of the max then my turbo 240, but i was wrong. Thats the price you pay for comfort.



Ditto the post directly below mine!

 

Yup I've been averaging about the same. I've stopped tracking because i hate seeing 16 or 17 when I calculate it.

 

If you warm your car up longer, leave it running to run in somewhere, this could be the cause in the cold weather we have had in the NE not much snow but really cold. I avarage about 18 in the winter in my 96 I30 during the winter and goes up to 20 average in the summer for city driving. EPA estimates for 5peed are 22 city 27 highway, auto 21 city 28 highway if I remember right.

 

My car, which throws no codes, this time of year gets somewhere about 18-20 mpg calculated correctly, 95% highway driving, mostly 75 mph using cruise control.
In the summer, it gets something like 22-23 under the same conditions as above.
Therefore I would say that your numbers are not unreasonable.

 

You might have a bad KS this won't trick the CEL. What happens when the KS is bad is that the ECM goes into safe mode and the sensors don't work to full potential. I would get your car scanned at Autozone for free and see if it throws a code. This was my case I was averaging 20-22 MPG city and it went down to 15-17. Replaced KS reset the ECM and it went back to normal. CHECK OUT THIS SITE IT IS REAL HELPFUL TO TRACK MPG http://www.fueleconomy.gov/

 

I had a brand new KS put in at 120k miles. It cant go bad already.

 

Maybe bad 02 sensor? Check for ghost codes.

 

Forgot to mention I changed all the primary O2 sensors as well.

 

i get like 190 per tank, maybe less , i dont give a dam, its a 6 cyl, man

and plus its old

 

^ Assuming that you put in lets say 16 gallons, thats around 11mpg. Thats horrible, you should really check your car.

 

Give it some time, when the weather gets better see if your gas mileage goes up. Its most likely the gas itself. Keep the RPMs low when the car is cold, I shift at 2K or lower until the temp is up to normal conditions. Im getting 23MPG but thats with a manual transmission which I hear yields better MPG.

 

man i cant even get 293 out of full tank with the car off. thats pretty good, i changed my spark plugs, two coils, ks, and two oxygen sensors when the car was throwing no codes and now i getting pretty good gas milage, mabe 280 verses the 200 i was getting.

 

Have you tried getting your fuel injectors cleaned professionally?

 

What can i say i just bough my maxima with 171,000 miles and it runs like a beast. It is the fastest car I ever owned but i'm PAYING for it at the pump. Agreed, my 95 maxima gets horrible gas milage also.

 

I get about 14mpg also...even with my feather foot. cant get past 250mi every fill up and when i buy gas its always 16.1-16.5 gal. I too am calculating milage correctly and it feels so bad. I wish there was something i could do but everything on the car is OK it just runs way too damn rich. I warm it up for about 3 min in the early morning before school and in the day/night i just start and drive off. I think its these 350z rims though...i cant really remember but i think that the week i had it without the rims i could get 400mi /tank and plus the ride was much smoother.

 

Have you tried getting your fuel injectors cleaned professionally?

 

its probably your rims descent, they look good, but they are a bit heavier if I remember correctly. Man i thought I was doing bad with 21 mpg city/highway average.

 

My fuel economy has also turned to **** a few months ago, for no apparent reason. It was good before and got very bad all of a sudden, so there's no way it's "normal" to get only 14mpg, especially with how conservatively I drive. Also, my fuel economy was good all last winter, so I'm sure it has nothing to do with winter gas. I have no CEL and absolutely no codes at all when I manually pull codes with an OBDII scan.

Since nothing else has helped so far, I am going to try getting the fuel injectors cleaned this week as dr-jrp has suggested to the original poster. Damn I hope it helps because 14mpg sucks.

I will post my results back to this thread in a couple of weeks once I have determined if it helped.

If anyone has any other good suggestions, please note the following items can be ruled out in my case because they have all been done in the past few months:

- New Air filter
- New Fuel filter
- New Coolant temp sensor
- New Spark Plugs (NGK Plats)
- New ignition coils (All 6)
- New PCV valve
- Cleaned Throttle body
- Cleaned IACV

Also note:
- I do not smell or see any signs of fuel leaks, either under the hood or when checking the ground under the car.
- I keep tires properly inflated at all times and check them regularly.
- I have verified that my brakes are not binding or anything like that which would create extra drag.
- I change oil/filter regularly (5w30)
- 90% of my driving is to/from work, and since I works nights, I am almost never driving in heavy stop and go traffic.
- I park my car indoors (both at home and at work) so I do not waste gas warming it up
- I use (and have always used) premium gas, 91 octane
- Fuel ecomomy was fine all last winter, as mentioned, so it's not a winter gas issue.
- No codes when checking ecu, so no reason to suspect failure of any specific sensor.
- My car is a 99 GXE, automatic, with 130,000Km (that's about 80,000 Miles)

 

Don't worry about it man. I have horrible gas sometimes too.

 

could it be that my rear tires are 245/50 and the fronts are 235/50? Fatter in the back because the Z is RWD but since the max is FWD i have a lot of extra drag now? If i were to get new tires maybe just in the back it would eliminate some of this drag?

 

don't know what you're all talking about. I did winter pizza delivery during school break..lowest gas mileage was 20 and I pushed her a lot. Highway with my grandma driving average out 28 mpg (60 mph right lane grandma fuel save mode).

Sometimes I think its just better to get a smaller car with weaker engine and go faster on highway while getting higher mpg still.

 

LOL

 

what viscosity oil did you put in at your last oil change? believe it or not, oil viscosity can have a significant impact on fuel economy - that's why honda and ford spec 5W20 now for CAFE reasons. I recently put Castol Syntec 0W30 (gold GC) in my VQ and I saw my fuel economy drop from 22 to 18mpg. Now you might say "but 0W30 is thinner than 5W30, right" -- well, no. GC is actually a very thick 30wt oil - thicker than almost every 5W30 on the market at every practical temperature. the 0W spec doesn't come into play until extremely cold temps (like -40). in fact, GC is to 5W30 as 5W30 is to 5W20. anyway, the point is if you put in thicker oil your mpg will drop. did you take it to a quick lube place -- they prolly put in 10W40!!

 

I replaced the air filter with a K&N this weekend and noticed an improvement in mileage.If I keep below 80 mph without any hard acceleration I can get close to 400 miles on a full tank. I got close to 320 on 3/4 tank with my check engine light on.
I can literally see my fuel gauge needle move if I'm speeding ( hard acceleration etc)
The car is a stock 1997 SE with 108K. I also bel. that he flex pc. is slightly busted and I may get a better mileage upon a replacement. It's left to be seen.

 

If you drive slow you'll get better gas mileage? NO KIDDING!

 

I have 4 brand new fuel injectors and the other 2 were from 99 max with low miles. I was wondering whether I unplugged some thing by accident when changing the solenoid valve but cant think of what. I would probably get a CEL if some thing was wrong, I checked manually and nothing. The car drives fine otherwise, cant complain about power. I also changed the coolant temp sensor and the PCV valve.

 

Anyone know how tires affect mileage? I'm referring to different tread patterns, not weight or inflation. Given the important of aerodynamic factors, I'll bet there are significant differences...

 

I was reading the honda insight has some special tire that has like no resistance. And when switching to a different/normal tire the mpg dropped like 5-10mpg or something crazy like that

 

I know what you mean about bad gas mileage! My max averages about 18.5 Mpg with all city driving. My 400+ AWHP EVO with much more aggressive driving (Drag racing at the Strip) averages 22.7 Mpg city driving. BTW the EVO runs 12.0@115 just to verify the HP. I love the max but this just doesn't make since. Oh yeah and I always run 93 Octane in both vehicles. The EVO also has Methanol injection over 10Psi of boost.

-Nate

 

Its all about technology that wasnt available at the time our cars were made. Most of the cars made nowadays get better mileage than ours and have more power to boot. Its life, deal with it.

Oh yeah, and enjoy your EVO you lucky bastard!

 

I just drove a hell of a lot the other day, 536 miles between Knoxville, TN, and Columbia, MD, and managed 27 mpg the first half of the trip, cruising at 75, and 30 mpg the second half of the trip cruising at about 70 with the windows open part of the time.

Shocked me, that's for sure.

 

I use nothing but Castrol Syntec 10w40 and I still peak at 30mpg on the highway, average of more around 28.

 

I just dont have the patience to "cruise", I think thats why I got stick in the first place. Putting the pedal down at 75 and actually feeling the car pick up speed as if it was doing 30 is just too much fun. Ill sacrifice gas mileage for pleasure any day of the week.

 

^ I know what you mean....I get horrible gas mileage too. The chevron techron did help me a little though.

 

i get like 19-20 in all city driving. i use 88 octane. better than the 12 i used to get with my lifted 85 nissan pickup