Warik

2k Auto Maxima getting 15.5 mpg city. Not a lot of stop & go and I've not been driving like an @$$ for weeks.

I've done the following:
- Replaced spark plugs & ignition coils
- Replaced MAF and had ECU reprogrammed
- Had ECU reprogrammed for new fuel settings
- Replaced fuel filter
- Cleaned TB
- Use Chevron Premium gas

Don't know what else to try. SES light is NOT on.

Yeah, I do drive with the A/C the entire time because it is insanely hot down here, but I used to get 18-19 mpg before, so there has to be something wrong.

What else could need replacing that wouldn't light up the SES light?

GBAUER

iTrader: (2)

try the PCV. $5 part and it might fix it.

KyMan

iTrader: (2)

For someone else not getting that good of gas mileage, what is the PCV and what does it do?

Teufelhunden

iTrader: (8)

try one of those prolong engine products.

FormorAccordMan

iTrader: (3)

try some auto-rx. it has a good rep, unlike the over the counter products

GBAUER

iTrader: (2)

the PCV valve is part of the emmisions system. It recirculates exhaust gas through the cylinders to help with combustion. Don't listen to the other guys above this post. Miricle fluids never work. You can also try checking your tires out as well. Are they full? Do they show any weird wear?

Warik

Tires are fine... I am using fairly new Kumho's ( ) and last time the tires were rotated (about 2 months ago) I was told they were wearing perfectly.

I've been experimenting with anything from 34 psi all around to 38 psi all around (tire says 44 psi max). No apparent difference. My original tires were inflated to Nissan's specifications before, but I noticed improved fuel economy when I increased it, so I never went back.

I will try the PCV. For $5 it is worth a shot.

Anything else I might want to try?

I'm inclined to stay away from the magic engine products since I believe Seafoam and Auto-rx recommend an oil change shortly after use. I just switched to Mobil 1 SS less than 1k miles ago and don't plan to throw it away. Maybe if I still have the same problem after 5000-7500 miles, I'll use the products next oil change.

Lontar1

iTrader: (5)

In reality there is not much you can do.. you own a gas drinker and you best option will be stop the car..... I know I did.... too much money on gas for my 100 mile commute. Trust me I tried every trick on the book and the best I got was 24 mpg highway all the time..... and the average was like 19-20 mpg... which sucks.... right now I drive a 94 Toyota which has 122K miles and still make 34mpg.....

Belteshazzar

PCV = Positive Crankcase Ventilation

Combustion gases accumulate in the crankcase no matter how tight your engine is. The PCV valve allows your motor to inhale and burn them. If I was forced to draw a connection, not evacuating the pressure in your crankcase could allow it to build up pressure and produce a pumping loss, but that's a stretch.

Sorry that's not exactly any help, but to say don't get your hopes up.

Belteshazzar

You didn't specifically say your air filter was good though I'm sure you checked it.

You did right?

AllMaxxedOut

iTrader: (15)

Check your knock sensor and change if bad. That usually leads to bad overall gas mileage.

steven88

iTrader: (28)

your car is doing fine...I get 16mpg all city...I do have a heavy foot and drive VERY short trips....there is no way around it...if you drive in the city, you will get bad mileage PERIOD....I tried this on a few different cars....one being my old 96 maxima, my current 2k2 maxima...and my mother's 2005 toyota camry....ALL CARS will get bad mileage if driven ALL city mileage...

Warik

Belteshazzar:

Sorry - changed air filter when I changed the MAF. Also installed in-cabin microfilter if that's relevant.

AllMaxxedOut:

Won't a bad KS throw a check engine light? If not, how can I tell if it's bad?

steven88:

I would agree with you if I had always been getting 15.5 mpg... but I haven't. If I was getting 18-19 mpg city (with worse traffic than I'm driving in now) for as long as I can remember, then the only thing I can think of that could explain a 2-3 mpg drop would be something wrong with the car. Lontar1's comment about his Toyota getting 34 mpg after a 120k+ miles should be indicative that age alone will not reduce mileage.

Besides... my Maxima isn't old at all. Only 54k miles with no performance mods.

steven88

iTrader: (28)

how long have you had your car? also what brand oil are u using? and what weight is it?

Warik

How long: Bought brand new in Sept of 2000. 54k miles as of today.

Oil: Mobil 1 Super Synthetic 10W30 (I was told to use 10W30 since the temperature never goes below 40 F here, so 5W30 is not needed. The 10W30 is new, as well as the synthetic. Used to use 5W30 cheap dino oil and was still having the mileage problem).

2k1seae

iTrader: (1)

This is just my experience FWIW. Every 2 years, I have service dept (my service dept has been good) do a fuel induction service. Cleans the FI's and throttle body. I'm currently getting 16.5 - 17.5 all city driving - 27 - 29 all highway. I see that you have cleaned your TB, but the induction service might do a little more. Just a suggestion ...

GBAUER

iTrader: (2)

That and possibly a clogged cat as well. Are you also losing a lot of power?

MaxSE-R

when was your last oil change? maybe you're overdue, i know i was getting that kind of gas milage before, then i change my oil and better now, i've been driving alot to school and i'm averaging about 30 mpg highway, but mix driving is about 24-25.

You can also try using gas from another gas station. my friend at UTI has been testing gas from different gas station and have notice that alot of gas station are diluting the gas by adding water to it. this might be the cause of your bad mpg.

chr0nos

iTrader: (1)

winter gas may affect it by about 1mpg or so. i know my milage dropped a bit. i understand that fuel system cleaners may do some good. best bet is to use before an oil change, and then change motor oil and filter.

YuAnChen

iTrader: (1)

I have a bad fuel economy too
my car is 01 and at 122k km
just finish dear 120k service
doing fuel filter soon
and i will try to do above idea provide above thanks
and is the ignition coils really matters ?
cause i dont see a gray dot on my ignition coil.
I also dont know if the MAF is replaced or not
Cause Car bought 110k Km
Thanks guys

Forgot to say my fuel economy is about 5.5 KM/Liter

Moreno

And I thought I had bad fuel consumption but I guess it's average 8km/l or 17.5 mpg/g.

spirilis

iTrader: (2)

Heh, my 2000 5spd gets around 26-28mpg mostly highway.

Do you know what type of condition your upstream O2 sensors are in? Maybe someone with an OBD-II scantool that reads sensors could help; watch the O2 sensor transitions to see if it's really sluggish? I replaced my upstream sensors after 105K miles and the O2S transitions occurred a good bit faster.

Also, check for obvious stuff like disconnected hoses/vacuum leaks/etc.. If you do have a buddy with a decent OBD-II scantool that reads sensors, peek at the Long Term Fuel Trim readings. I believe their range is supposed to be -25% to 25%, if it's lieing more towards the 25% range most of the time, something may be amiss ("25%" means the ECU is prone to richening the fuel mixture a lot to compensate for a detected lean condition; "-25%" likewise would mean that it's leaning out the fuel mixture to compensate for a detected tendency to run rich)

One thing you haven't mentioned so far is a compression check. That's really something that should have been considered first above all. Have a mechanic pull your coils/plugs and check the compression on all cylinders to determine if you have a compression leak. That will shoot your fuel economy down in short order.

n3985

iTrader: (36)

So on 8 gallons of gas filled into the tank, I got 70 miles before DTE became ---. Anyone want to tackle as to why my mileage sucks? I rarely if ever go above 2,500rpm, but do 2-3min short trips daily to and from school. Oh, and the heater was set to ECON.

Whtmax'01

last time i checked i got only 210 miles out of 15 gallons of gas so thats 14 mpg in the city. On the highway i get about 26 mpg. I have pretty much new spark plugs, ignition coils, maf, tires, pcv valve. Just learned to live with it.

DrKlop

iTrader: (3)

surprisingly Auto-rx does work. I also thought that it would not work the first time I heard about it, but I found enough info to convince myself that in does work and it's indeed very useful engine cleaner.

Jaws

You probably are getting really crappy mileage. Are you getting 17.5 miles per US or imperial gallon? BTW, if you are quoting metric consumption, its in litres/hundred km, not km/L.

FWIW Here's the consumption I usually get (L/100 km)
8 is good highway, 9 is average/winter highway, 10 is combined, 11 is city.

rule da road

THIS is THE thread. I am calculating the same. I have a ypipe, intake, new MAF, timing at 17, MANUAL, 85% HWY driving and get about 18 MPG. I use 93 in NY which is 10% ethanol but .10 cents cheaper than ANY one else. I'm PISSED. Every oil change i suggest MOTO Flush by my tech says no i dont need it. I'm really about to get the TORNADO!!!

bigEL

Had Nissan moved to direct ingition by 2000? When my old car suddenly got bad mileage, it turned out to be a bad distributor. Otherwise, maybe just a bad tank of gas. If your next tank from a different gas station still gives you bad mileage, I'd start to suspect something else. I've seen bad crank position sensors cause bad mileage. It doesn't trigger any warning lights as far as I know. I don't see a bad PCV causing bad mileage. Can't think of anything else off the top of my head. Maybe check for hidden codes. Good luck.

maximaownsyou

try B-12 chemtool, that stuff works great, you might smell a little bit of stuff (everything burning off) but you should be fine. i suprisingly get about 24 avg mpg 70%highway 30% city. if i grandma my car i get 400 miles to the tank if i drive it how i want it i get about 270-285 miles to the tank

pepemax

I am trying to chase something like this myself.

I will post my problem soon.

NmexMAX

iTrader: (22)

After 6 more posts.. or a thread jack

maxima57O

We had a 2000 blazer that was getting 12mpg highway. The problem was some type of coolant sensor. It was telling the engine that the car was still cold (like when you first start it in winter), even when it had been warmed up. It was a little over $100 to fix, and the highway mileage was back up to the regular 19mpg. Sadly, that mileage still sucks. I'm not sure of the exact name of the sensor, but if you describe it to someone who knows what they're talking about, they could probably tell you.

Belteshazzar

good call.

your blazer's coolant temp sensor was out/ reading incorrectly. Some cars realize this and fire off a service light, some do not.

KabirUTA13

iTrader: (11)

hmm i used to get around 350 miles to a full tank... now its dropped... my first gess is that i have a subwoofer system in the trunk which mite add to why i went from 350 to 290....some of the ideas put out are really good and im thinking about doing the same as well....

the paragon

iTrader: (11)

change your PCV valve and then do the PCV oil reservoir mod, i'm getting roughly about 340-355 per tankful

KyMan

iTrader: (2)

what is the PCV oil reservoir mod? I've never heard of it.

the paragon

iTrader: (11)

http://forums.maxima.org/showthread.php?t=417081

http://forums.maxima.org/showthread....+reservoir+mod

Warik

Not really... I'm experiencing a slight DELAY in power though... as in, if I'm doing 20-30 mph and I floor it, it will take about a second for the car to realize "uh oh, time to go!" and then my back is into the seat and it zooms off.

Could that be related?

Warik

Responses to various points made by others:

1 - Last oil change was < 1k miles ago and I switched to Mobil 1 SS. Can't be the oil.

2 - Can't be the gas station... this is the first time I've used Chevron. Used to use Citgo religiously, then switched to BP for a few weeks, then back to Citgo, and now Chevron. Always used premium. No change.

3 - I don't recall WHEN I started having this problem, but I know it had to have been in or before October (I know this because I filled up at a Shell gas station, which was the only one that was open near my house after Hurricane Wilma, and I commented to my dad after my next fillup about how Shell gas sucks because my mileage went down). When does "winter gas" come into play? (And still... ok, maybe I'll lose 1mpg from winter gas... but 2-3? Nahhhh can't be)

4 - Someone mentioned Knock Sensor. How can I tell if my KS is bad if I have no CEL?

5 - Going to replace the PCV valve and possibly do the oil reservoir mod. Will refill tank on Friday after installing new struts/springs and getting an alignment. I'll report back to this thread when I fill up again after that and check the milage.

spirilis

iTrader: (2)

Nissan's used Direct Ignition since at least the 3rd gen days, maybe before? I know they started using it in a number of platforms since the late 80's.