..and it used to be at 29.5 highway and about 24 city.

I wonder what sensors should I change since there is no CEL. I read the Haynes manual and it stated that the ECU is running with open-loop mode until the 02 sensors warmed up (thus burning more fuel).

I did not notice any driveability problems, no rough idle, no surging when you are holding the accelarator steady, except I could feel that the car is more responsive (due to more fuel burned?).

Will CEL always light up when you need to change your 02 sensors? My car is 97 and I did replace one sensor in 2001.

What else could cause this significant drop in mpg?


Thanks your help, as always!

 

wow, i know a couple of people here are gonna think you're crying about nothing. A lot of us only get 20mpg on the highway (21 if i'm lucky). I don't think my max has EVER gotten more then 25mpg.

but for starters you could try a new air filter, fuel filter, and clean the TB. those are all cheap and easy things that help gas mileage. also check you tire pressure.

 

wha what ???? your lucky i wish my car gave me that mpg $hit !!

poor you ....

 

I own two 1995 Maximas since new. Both have manual transmission. One SE and one GXE. The best mileage I have even gotten on the highway is 24mpg (at 80mph). Mixed city/highway give me around 22mpg.

I have no idea how you get 29.5. Can you explain to us how you calculate the gas mileage, and tell us the conditions (speed, altitude, number of passenger, manual/auto, ...) in which you achieved that extreme gas mileage? I would love to duplicate your experience.

Sam

 

It's winter, expect you MPGs to go down 10-20%.


Dave

 

Dave,

I agree....except even if I drive my car to warmer climates (40F and above) the mpg is still the same....(23mpg).

In previous winters, my car will go about 27mpg in the winter with a little bit of city driving. But 23???? and no CEL??

 

Hello Sam,

Sure. Here it goes, the car is 1997 GXE Auto Max bought at 88k (2001) and now it's at 146k.

My route is usually 99% all highway, with little city driving. I cruise at 74mph (yes, 74, not 75) most of the time. The car recently had its TB cleaned and new KS installed. Modification includes njmaxseltd intake "cheesing" mod, y-pipe, UDP, snow tires/summer tires, hyperground and K&N panel filter

If I cruise at 80mpg, I will get around 27 or 28mpg. I did this whenever I am passing by Penn. on the way from Milwaukee to NYC. As a matter of fact, when I am in NYC, I only get around 22-23mpg city/highway...so I believe that's the normal average for NYC.

I fill up my tank with either 91 or 89, but 95% it's 91, Mobil brand. I don't top off the tank, only rounding it up to the nearest dollar. I get my mpg by dividing the mileage driven with the gallon filled.

Here is my "normal" route. If you fill up the tank until the pump stops automatically, the gas gauge will go beyond F mark. If you were me, I will see the gauge will get to F mark once I am travelled exactly 74 miles (cruising at 74mph) from where I start. It will go to the the end of the letter "F" when I traveled 124 miles. If I continue travelling (still in the highway), I will see 176 miles coming up when the gauge reaches 3/4 full. When the gauge is at half mark, the mileage would be around 255 to 260. If I continue travelling from here, the 1/4 full mark will come when I reach 400 or a little bit more. If I continue travelling from here....I will search for the nearest mobil gas station.

My gf also has a Max, but she lives in San Diego. Whenever I drive her car, the numbers above still hold true, although I usually cruise at around 78mph instead of 74. Hers is a stock SE automatic though...

I usually drive with no passengers......Altitude wise..hm..I don't know, but I don't suppose we have that many hill here around Milwaukee. I store my car in a heated garage.....if you think it's a factor.

I am quite surprised when I saw several people commented on my gas mileage. It's the normal one I have collected in the past 2 years owning the car. The only time my car was giving less than 24 mpg consistently (no matter city of highway) was when I drove around in NYC, and when I "streched" the oil interval of Castrol Syntec to 8000 miles (the oil did not like it at all).

Tomorrow, the car's oil will be changed. I am hoping to get a Scanner/Reader for OBD II codes at the shop, there might be a hidden code in the ECU.

 

Guys,

Will

02 sensors
evap code
lean/rich condition in each bank

....ALWAYS trip the CEL? or not?

 

hi buddy
I get 15-17mpg, 90% city.

yes, my all my sensors are fine. KS recently replaced.

don't complain, thanks.

 

ardica,

Many thanks for sharing your data. I can't find anything wrong and/or unusual with your vehicle and your method. All I can say is that you and your girlfriend are lucky owners. Your mileages not only match but exceed the EPA rating (21/28). If mines were like yours in term of efficiency, I would have saved at least $1,000 in gas.

As far as hidden code, you could see them all (if any) by switching your ECU into diagnostic mode. No need for a 0BD II reader.

Sam

 

I don't think he's complaining, I think he's wondering why his mileage went down. I myself get ~ 360/tank with 95% highway driving, so our mpg are about the same. I don't think you should be too concerned about it since your car has high mileage, but obviously you'd rather have 27 mpg instead.

 

Gates,

Thanks for your post, I see complaining in the forums is like solving an algebrae problem by chewing bubble gum and nothing else.

Your 360 per tank is normal for you...but I usually get that when I get closer to 1/4 tank (i.e. still has about 4 more gallons to go).

The funny thing is, the car seems very responsive overall, definitely better throttle response in the highway. I could stay in OD without having to press the gas deeper in most cases which I often could not do normally (has "order" the tranny to engage 4th or 3rd gear to overtake hastily).

 

Sam,

That's cool with me. Yeah, I know about that ECU diagnosis thing. I usually do that, but someone stole my toolbox from the apartment garage this past week and I don't have any laying around. Since I am going to change the oil, might as well have the codes checked.

BTW, I think mpg really depends on how you drive. Overall, I think I am a "gas saver"...because I know my gf's car returns a lower mpg figure if she drives around with it.....(well, all that traffic jam on I-405 might be THE most affluent factor).......and I always drive long haul (100 miles or more, highway).

I think if you really want to, you could go to Milwaukee, give me a holla, and I will drive your car just the way I drive mine. That way I could give you a glimpse of achieving 29mpg with your car....

 

i remember getting 400 miles per tank back last summer. that equates to about 23.5mpg, now I only get 300 mpg

 

300mpg!

Yeah my gas milage went down during winter also. . . .I think its normal.

 

Mine's now down to probably about 400 per tank as well....from 500/high 490.

I realize that they change the formulation a little bit...but from 29 to 23?? Man... that's 20% and I drove around in WI, IN and IL from single digits up to 50F with no change in MPG.

 

Reason: Cold engine needs more fuel to start, warm up & run.

 

I get about 280 per tank, what could I do??

 

u have to be at like 60degrees + to not consider a loss in mileage, plus the gas is oxygenated now and that leads to worse mileages as well

 

All you people claiming over 400 mile per tank....is this when the needle reached "E" or when you drive the car until it completely runs out of gas and stalls

 

I just filled up and my mpg was 18.293 . This was with a mix of city and highway, mostly short trips. I have no stored codes, just checked two days ago. I will eventually brake down and get some new O2 sensors. I am almost at 129k with the original ones. Good luck on your search for higher mileage.

 

I wish I could get at least 300mi to a tank. I get less than 200 I got two new front o2 sensors sitting in my closet. Its too cold to put them in, and I might wait till I get my wsp y-pipe. I hope the o2 sensors fix it.

 

right now with the snow out im at 50 miles with 3/4 of a tank left it sux lol but its cuz of all the snow and the cold

 

back when i was getting 400 mpt, i was pushing it, at about 405 miles the fuel light would come on. That was 98% highway driving during road trips over the summer. Mix a little more city in there and it goes down drastically

 

That's about the shortest answer you can get for people getting 400 and others wondering how they get that..City driving absolutely sucks gas

 

ardica,

Agreed, mpg depends on how one drives. But that only applies to city driving. On the highway, there is no difference unless the driver is ignorant or intentionally wants to waste fuel. On the highway, I cruise in 5th gears and use cruise control. My vehicle is well tuned, so there is nothing else I can do to improve mileage.

The only difference between my car (manual) and yours (auto) is that at at the same highway speed, your engine runs at a lower rpm (about 7% lower), which results in a LITTLE better mileage.

Anyway, let's hope that there is a code in your ECU, so you can remedy the problem and get back to your excellent gas mileage. Best of luck.

Sam

 

another thing, i recommend pullin the plugs n checking the condition of them. Esp look for a carbon fouled plug. There seems to be a tendency for the injector to stick open or the coil pack to loose its strength. I've had this problem and the mpg does down.

 

cough...cough....Tom....cough.....would this be attributed to your cheesing tecnique for the intake tract? cough......



Yeah, I know about the car warming up and so on..... but it's still excessive for me. Oh well, just ran the car for codes...no codes whatsoever.

 

I've never driven the car until it stalls. That way, you are putting a shorter life on your fuel pump because it has to work extra hard to suck those fumes and what's not in the bottom of your tank.

You could drive my car and get 400 per tank without having it to stall, under my driving condition, though...

 

Sam,

Yup...I haven't driven a manual over a long haul just yet..... I was eyeing an SE with 5-speed but it was bought even before I called the dealership.

About my highway driving, I notice a lot of difference if my car goes to the "hilly" side, like I-70 in Colorado, from Denver to Grand Junction. In this case, leaving the car in cruise control will make it shift back and forth from 5th (overdrive) to 4th constantly. My observed mpg will go down when I continue driving like this. The best way (but not necessarily saving gas) is to turn off OD (limited to 3rd, no 4th and 5th) and revert to manual throttle (no cruise control).

The car is having an oil change now, hopefully it solves the problem...

Thanks for posting guys! I really enjoy your insights and comments!

 

ardica,

Just FYI: You don't have a 5th gear. Your 4th gear is your overdrive.

Sam

 

I never done 490 per tank ,but I did 430 when the fuel light came on...Now ,in the winter time the mileage went under (I still get 24-25 miles combined) but is not too bad. It s very cold in Ny and I use 4 Dunlop Graspic tires...The soft compound it takes a bit of performance away , but the travel in the snow is quite easy . I ve got a 5 speed 96 Se with 146 k ,with almost new KS and upstream sensors . My gas needle moves almost the same as Ardika s .I don t understand why some folks get only 300 (or less) per tank...Just remember that if there is a bad o2 heater ,your car is going to run in the safe mode (No Cel) and the gas mileage would suffer. If you have an identical problem , plus cold weather , plus heavy foot and a little snow, those may be the reasons of bad mileage

 

Sam,

Yes, as stated in my post, OD off is limited to 3rd only. 4th and 5th are overdrive, with 5th is when the TQ lock the gear.

Oh...btw, not to be nitpicking...it's with "k" ...not "c".

 

Astil,

Thank you, your post is very interesting. You said that if the car has a bad 02, the engine will run in safe mode.

What is this "safe" mode? Is this the same with "limping to home" mode, where the engine rpm would not go about 2000 or 3000 rpm?

Or do you mean "open loop" mode, where the ECU disregards inputs from both 02 sensors and just rely on MAF and KS sensors to operate the engine?

Because...mine will still rev to redline anyday if you are asking it. So, I guess I don't know how to determine when the engine is in "safe" mode and/or "open-loop" mode.

Glad I know that your gauge needle is about the same as mine.

 

Sorry...Open loop is the right word...Haynes manual offers an excellent detail regarding the O2 function and features. I don t have it next to me to pinpoint the word exactly. Anyway, no matter what, a bad O2 sensor or a bad O2 sensor heater IS NOT doing good for our cars and for our gas mileage. The safe mode is when the KS sensor is bad ,and the timing is advanced only so much. Sorry for the mistake.

 

Well...well..well.... seems to me that oil is the culprit here. I was running my 2nd Auto Rx bottle and the instruction states to change the oil within 1000 miles for the second treatment. I somehow misinterpreted it...and went on to 2000 miles. Have to read more carefully next time.

Now the car has new oil in it, the mpg is back to normal even though it's pretty cold out there in Milwaukee/Madison, WI at the moment. The funny thing was the guy at the shop screwed up and did not put my Castrol GTX in the car, instead, they put their Mobil oil in there (no charge). I need to go back next week or the week after to have them fill in my car with the GTX.

Seems to me that my car has a very strong relation between mpg and oil condition and/or oil filter filtration. I know that a lab test would probably show this, but I did not send any sample from Auto Rx usage to the lab (so I can't prove my "theory" scientifically).

Another interesting point was, I just remembered posting another thread about mpg vs oil age in this thread back in April of last year.

http://forums.maxima.org/showthread.php?p=1928893

I will post again to let you guys know if my mpg holds.........but I really appreciate all who posted their takes on this issue. The .org has been THE place for me seeking consultation regarding Maxima's maintenance and mods, so hopefully this thread will somehow be useful in the future.

 

Nismos14 probably hit a major contributor when he mentioned oxygenated gas. Saves on emissions in the cold weather, but results in lower mileage. Also factor any extended warm up time, and double check your tire pressure. Tires will lose about 1 psi for every 10 degree F drop in ambient temp. Add that to the 1 psi/month average loss, and you could have really underinflated tires without noticing.
Like most of the others, I think your mileage isn't bad. But I can see why you would want to know why it has dropped.

Dave

 

wow guys,, im lucky if i get 220miles per full tank

 

My 97 Se 5 speed gets 29 on the highway. i use Amoco 93 octane.My 3rd gen. got the exact same mileage.I'm happy!!!!!!