MaxDD

99 Maxima, all stock, 92k miles.
New: fuel filter and air filter, plugs are fairly new

I'm only seeing about 17 mpg (mixed city/highway). I DO have a CEL currently, for the rear o2 sensor (Fed emissions - not CA). I was told this sensor has NOTHING to do with engine performance/fuel management.

What else can I check regarding my mpg? Car drives smooth and is in great unmolested shape. Only other odd thing it does is idle at 2,000 rpms every once in a while, but will calm itself done within a couple minutes. Could this be the IACV?

I own another Nissan, so I'm familiar with "Nissan quirks"

Thanks in Advance

nsnrider

iTrader: (59)

replace you primary oxygen sensors, clean the maf and iacv.

ease up on the right foot.

done.

MaxDD

Front two o2 sensors were just changed about 2k miles ago.
I don't know this car's engine bay too well yet, where is its IACV?
I'm skeptical about cleaning the MAF sensor, but maybe I'll give that a try. What do you use, that CNC stuff?

njmaxseltd

iTrader: (19)

How are you measuring MPG? Full tank of fuel used? What's the driving conditions, city, highway? How long is your commute? In general, all of these matter. Combine those with very cold winter temps and your MPG suffers. When's the last time you checked tire pressures?

Justaguy

I've cleaned the MAF, IACV, throttle, EGR,replaced 2 sensors, I don't have any codes, seafoamed, changed sparks, oil, filter, I use premium gas, tire pressure good, I drive like a granny and I get 20mpg at best (measured by writing the mileage down, reset, fill tank,drive till tank almost empty, take mileage and calculate). There is nothing else to change unless my wiring is faulty...I gave up.

I hope you find something!

ACee

Check your wiring. Look real close particularly around the camshaft and other electrical connectors. I had a similar problem and found dry rotted wire sheathing showing exposed copper wiring that was touching.

nsnrider

iTrader: (59)

how many miles on the car?

you might have leaking fuel injectors or dirty for that matter.

MaxDD

Justaguy thread jacked me lol. Tire pressure is good. 92k miles on the car. My commute is 13 miles each way. I do let the car warm up... but I was seeing poor mpg even in warmer weather.
I'm stumped... I will take acee's advice and check wiring. however the car is unmolested and in good "shape" so I don't see why I'd have any bad wiring.

ACee

Cleaning the maf is easy. Follow instructions on the can and you can also find threads here on the org that walk you through it.

With no codes it has to be some sort of trouble shoot for intermittent problem which can be the most difficult.

MaxDD

I do have a code. its the rear o2 sensor which i first stated in the thread

skaterdudz02

I don't entirely agree that rear 02 sensors don't affect gas mileage. Your best bet would be to hook up a scanner and monitor fuel trims at idle and while driving.

Shouldn't be but + or - 10% each way.


I say you should change out that faulty 02 sensor and go from there.

ACee

I must have imagined seeing that you have no codes. The rear o2 however doesn't affect gas mileage (my apologies if this is already stated).

I personally would replace it though. To get rid of the ses light.

I read "no codes" is justaguy's post. Sorry. I realize it is not the op now.

ACee

Unless the rear o2 code is pointing to a catalyst inefficiency.... if it is, then the bad cat could be choking the exhaust flow and cause poor mpg.

MaxDD

Yea i was also thinking maybe exhaust related, causing the o2 to fail or give faulty signal to the ecu. the exhaust looks like an odd design, right? are there aftermarket exhaust pieces that streamline the stock design? if that makes sense haha

Justaguy

MaxDD, so sorry about the hijack and confusion it caused.
My bad.
Sorry.

97_GXE

92k for a 15 year old car sounds like it doesn't get out enough. These cars are designed for long trips. Mixed city/hwy won't get your best gas mileage. 17 mpg is about normal for this car according to fuel economy.gov and Edmunds. If you want good gas mileage, fill up and drive 450 miles straight highway stopping only for bathroom breaks. That should be around 25-29 mpg.

I get bad city millage, but I can go awhile without filling up on road trips. Another thing, is maybe change your gas station. I kid you not, but once in awhile ill get duped with some crap gasoline. I should be able to do 160 miles from a full tank to 3/4 tank going 75 on highway. some of these no name gas stations (excluding grocery store brands which I think are pretty good) have only netted me 120-130 miles.

Sounds like your car needs an italian tuneup: long roadtrip to burn off gunk and some pedal to the medal. You say you drive like a granny, when was the last time you hit the redline at 192 HP?

MaxDD

I don't drive like a granny, that was the other guy who posted that.
The car has been in my family since 14k miles. My mother did drive like a granny though, and it wasn't driven much.
However, I've owned the car for about 10 months and have put on roughly 6k miles. I hit the gas enough, and def use the car's power potential.
I also use different gas stations, but I do agree with that suggestion.
I've also replaced the gas cap, just another piece of info to add.

MaxDD

o2 fuse checked out ok.

230

I have a 1995 maxima that generally gets around 300-330 miles per fill up.

Normally average 20-22 miles per gallon. I drive 52 miles round trip to work which consists of 90 percent highway driving. I have never driven over 350 miles on a single tank of gas. Normally put 15 or 16 gallons in every fill up (high grade gas most of the time).

I know this does not help much but just trying to offer some small insight into your situation.

dwapenyi

iTrader: (3)

Maybe your commute is too short. How long does it take, and when u warmup, how long for?

Also, try TCW3. I'm not into additives at all but I LOVE TCW3. Maybe something in your car isnt running quite optimally like a sticky fuel injector etc;

http://forums.maxima.org/fluids-lubr...itive-new.html

dwapenyi

iTrader: (3)

20-22 mpg on a 52 mile roundtrip with 90% highway is low....you should be getting 25 or better. Are you going way fast? Big rims or oem wheels?

230

I have the stock 15" honeycomb rims. I do like to go around 65 - 75 miles per hour on the interstate.

dwapenyi

iTrader: (3)

Assuming all other maintenance items are done (air/fuel filters, plugs etc) replace your primary O2s. You should notice better mileage AND power. Tired O2s wont throw a CEL but they will act sluggishly, making the car not run optimally.

230

Thanks for the expertise! I have not replaced an 02 sensor on this maxima. This is why I frequent this forum. Cheers.

maxgtr2000

iTrader: (29)

Tire pressure is a factor also in mpg. Air molecules compact in cooler weather. With all the arctic weather the nation has been having, your tire pressure that used to be 32 psi+ is less than that. Contrary to that, airliners and drag cars run less air pressure in the tire because when it heats up the air expands.