Ok, where to begin. I bought this car a few weeks ago in order to keep the miles off of my WRX and to save money in gas. Well, I have been doing some reading that some of you guys are getting well over 300 miles to a tank of gas. I have filled up a few times now and have been getting right around 240 miles each time. I was wondering what I need to check/replace in order to get the mileage up. I know the car is definately running rich by the exhaust smelling like fuel, but I have already replaced the O2 sensor. It ran clean smelling for about 100 miles then back to the same ol stinkyness. I really think it was running fine because I reset the ECU (not because I replaced the o2 sensor) and it "learned" over the 100 miles and converted back to the prior settings. I guess I don't know if I just got a bad "new" o2 sensor or if there is another part bad. What else could be the culprit? Knock sensor? MAF? Well, thanks for the help in advance.

 

I feel you man . I have been disturbed about my mileage ever since I have gotten mine and it seems like the only thing that has made any bit of difference is the kind of gas I use and that is minimal at best. I usually am around 260ish at the end of my tank and that's after fuel filter, 02 sensor, spark plugs and better gas. I am with you and would also like to know what's up. There must be something that can change this garbage

 

I changed my fuel filter, spark plugs, and I put higher octane gas in my car to see what happens, and I still only get about 200mpg. I add additives like BG44k (I think thats what it's called) and I get about 20-50 more miles.

 

And I though My car was a dirty drinker.

I have honed just about every piece, and now get on higway (70mph) about 440 miles per tankful. City is somewher 300miles per tankful. And then, our gvmt robs three times the price you guys pay...
- spark: wires, cap, plugs; all filters, all wiring connectors, the tiny ctrl hoses, Throttle pos sensor, idle circuit& throttle clean...

I suspect my rear brake does not let go sometimes after braking - used to smell but not anymore.

Btw. A lot depends ont the captains foot. Maximas horses are thirsty if awakened.

 

:kekeke: I get 100 miles per 1/4 tank

 

The best you can do is tune it up well (since you have a VG) check your tire inflation and try to go easy on the accelerator, like Wiking said.

After that, adding things like an intake and less restrictive exhaust will help. When I put on my y-pipe, I noticed a few mpg increase. Same with my intake. Another part of that might be a partially clogged cat, too, which might explain why your exhaust smells.

If I drive my car carefully, I get about 30 mpg. When I stomp on it a lot and high tail it around town, it drops to around 20 mpg.

 

My car runs fine on cheap gas. Does anyone actually see a mileage increase with Premium?

 

here's another wrench to throw into the mix.
what condition are your axles in?
if they are worn/bad they can and will reduce your mileage.
one of these days I'll replace mine.

 

Octane doesnt influence gas consumption. If you advance ignition (more pwr), higher octane is needed - just for the engine not to break.

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----> "exhaust smells."

My maxima VG30E Used to stink after a highway stint like all army rubberboots were on pile&fire. Brakes not hot... No clue where it came from. Now u say clogged cat...
1. cat clogged by by mouses or what???
2. Now. Stink no more. Mouses escaped the cat???

1+2=Lapland Magic or can you educate me more on the cat and its lifetime behaviour? ...see, tis my first cat, only dogs before...

What I've learned that the cat even does not become functional (low rev) as I drive 10min. to the inspection 50mph; one has to rev 4000 for few minutes to get it doing its job and the emission tests through. All this means it is mostly dysfunctional crap tincan... = I pay the expensive candy for greenies.

 

a catalytic converter can get clogged by having too much raw fuel, which melts the catalyst brick.
the catalytic conveter starts working at approx. 400*F
read this for more info on the converter and how it works

 

Really wish people would stop equating advancing timing to more power - its only true if your timing is not already optimal and can in fact be totally counter productive in most situations.

 

...wishful thinking not granted.

In maxima global setting case the 15 degrees /92octane is not the optimum if -maxima- people wish for power... but somewhat more. With 20 degrees higher octane should be used. I use VG30E advance at 17,5 which -gives more power- than well wishers ever know...

Everyone does with his own whatever he wishes... one can break any car without knowledge, even with TDC.

 

so back to the topic at hand of bad mileage

any other ideas?

 

wow your cats and dog and mouse story is wacked! lol

about the axle, i was told my axles need replaced, but i dont think so, i mean the boots are ripped, but other than that, i think they are ok (wishful thinking) and i get about 28mpg or so.

aw89maxSE, are you driving only in town, becuase that could be your big problem with bad gas milage.

 

What other things should I be looking for??? Its not worth it to me to drive a car that is more expensive than my daily driver. I really need to get this taken care of. By the way, thanks to everyone for all the post....Keep'm coming!

 

You guys with bad mpg - sure you running the intended engine ECU and not a replacement?

Example - in South Africa we do not have emission legislation yet - and on the local ECUs in this country, the O2 sensor that is normally said to partially control mixture, is not even installed at all - ie - the MAF, TPS and engine coolant temp are most likely the only obvious mixture governing parameters -

 

Octane can change fuel mileage, because with higher octane, especially in a higher compression engine, the combustion is more complete, which gives more power and less fuel wasted in the combustion cycle. Over the course of a tank of gas, this increase in mileage should be felt, it'll be small, maybe 30-50 miles or so, but nonetheless, it's there. You may notice it more on the highway. Sometimes even standard compression engines can experience minor increases in milage if higher octane is used.

Tire pressure is very important, and one of the most common things overlooked with mileage. Making sure all your tires are at optimal pressure insures the least amount of rolling resistance possible and should increase mileage. The time to be most aware of your tire pressure is during seasonal temperature change, spring to summer, summer to fall, fall to winter and winter to spring. That's when the most dramatic temerpature changes occur, and the most dramatic tire pressure change will result.

Most areas of North America are experiencing winter temepratures right now, therefore that's going to hamper mileage. Your warm up time is increased, so you might be doing more idling, driving slower because of snow and other weather, and the like which all help to hamper mileage. Oil also becomes thicker, switching to a ligher weight oil in winter like 5w30 will help. I think all Maximas tend to recommend 5w30 year round anyhow, and with the new SL oils, 5w30 should be good in most heat and cold except for extreme conditions.

Driving style is very important. Speed on the freeway can also make a difference. Keeping a relatively constant speed, or change between different speeds being very smooth, makes a big difference. Driving at the speed limit is a relatively efficient speed, but pushing the limit can reduce mileage drastically. Since you're used to the power of a WRX you might be putting your foot into the Maxima a bit more than you think, conseqently affecting mileage. The 02 sensor thing sounds weird though, if the gas smell is back, have it looked into, maybe the replacement went bad prematurely. Bad 02 sensors will reduce milage.

 

Octane doesn't to diddly. You do know higher octane means slower burning right?

I'd do a full tune up with plugs, dist, wires etc. Check all vacuum lines pcv and egr.

If your engine has been beat up and is worn out, not much you can do about it.

 

my maxima has never gotten "great" mileage. and i've stopped caring. i don't think these cars get good mileage, no matter how well tuned up they are. the biggest thing that depletes gas quickly is aggressive driving. i'm addicted to it, so i just accept that my mileage sucks. and consider everything that everyone here has said, too. especially O2 and egr --valve that helps cool combustion chamber. if it's bad, detonation can occur.

a question arises at this point, to refresh my bad memory: if the car is running cheap gas, and/or has bad egr, this leads to detonation and knock, right? so wouldn't the knock sensor be acting up, retarding the timing and making it run like ****? and if it's too rich, as already said in this thread, this can lead to the catalytic destruction/ obstruction and/ or bad spark ----- result -----> runs like ****.

 

yeah I do and I know you're probably right in thinking that has a lot to do with it

 

The link was good, thanks! However, the theoretical issue was not my problem, but how the cat behaves in my car when 10 yrs old...

The theory was that our -cat age- would get all cars greenclean. But the truth dawned, our wallets are now clean and our environment is full of the carcinogenic metals [censored] that these cats once contained. So howabout a black helicopter conspiracy story?

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Can you broaden this statement: "which melts the catalyst brick."

My car was super 70k as I got it 1½ yrs ago, all done by Nissan. However, time to time it was like the volvos [swe dish tractor], with black smoke after start. After few months of repairing one bit after another [ten years is too much for rubber parts & connectors], I lastly ended up rebuilding TPS. Now as I tuned it to operate from 1k-9kOhm & modified its cam to switch the kickdown at 2/3, its response is like a dream. (btw, TPS has never worked as its specs say)

Could my story mean that the cat was really 'filled with mouses', and during driving some 4000miles, soot has burned off? [maxima not smelly anymore]. The emission inspection was all best, with second try with the faulty TPS. Cat has to be ok...

The reason I go after this, is the terrible smell my car had for few months(I really thought it was on fire!), but never seen any cause for it. Could soot filled cat have been the only cause? (I thought the rotten egg smell was beacuse of cat, this stink I had was like burning 'rubber'...)


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Btw, forum: My opinion (based on other wise men) is that rising your octane level does not help in gas consumption.

Info from : http://www.ourautoshop.com/GasFacts.html

What grade of gas should you buy?
87 Octane? 91 Octane? What do I need? Rule of thumb here is to buy the lowest octane gas that your car doesn't ping on. Today's very sophisticated electronics constantly adjust the timing of the engine to prevent pinging (detonation). If you buy too low of an octane fuel, the electronics detect the pinging and retard the timing. Retarded timing equals less power, and less available power equals more pedal.
It's a viscous circle. Pay more per gallon or pay by buying more gallons - you decide. By the way, detonation means just that - the fuel is literally exploding before the engine ignites it. This can have serious effects on your engine such as high pollution levels, destroyed catalytic converters, destroyed engine internal parts, and, need I say, puts a really BIG dent in your wallet.
Consult your owner's manual to see what was recommended from the manufacturer. Often the recommendations are higher than you can find. In that case, go by the "no ping" method.
Contrary to popular belief, the lower the octane number, the more explosive power it has. High-octane fuels burn slower, thus allowing a cooler burn. Cooler burning fuels mean less pinging and fewer emissions. Using high-octane fuel in a vehicle that doesn't need it is just a waste of money
No performance gain there!


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So the higher octane, the earlier you can put your ignition timing without knock sensor/ECU retarding the ingnition. Global setting in maxima is 15 degrees using 92 octane that is available in most countries (russian doubt). Here we have only 97 & 99, so advancing the timing to 17,5-20 degrees BTDC does not cause problems but -gives power in VG30E.

 

Thanks for the post everyone, but seriously back to the topic at hand.....gas mileage fixes remember?

 

these all were related to possible causes of lost mileage.
the best thing to do is fix every stupid little mechanical problem on the car and then realize that your mileage just went up.
ANY malfunctioning drivetrain component whether it be tires, brakes, fuel injectors Catalytic converter, computer or sensors. they can all and in most case will affect your overall gas mileage.

 

It's interesting that my 91 SE after 213,000 miles still has no smell to the exhaust. I guess the previous owner(older school teacher) took extra good care of the car always serviced at Nissan. The exhaust coming out of the exhaust tips is nothing but hot steamy feeling air. It is odorless and even the inside of muffler and tips looks brand new. No black soot or buildup of anything.

 

Err...have you ever idled your car in an enclosed space? Exhaust gases HAVE to smell. The only ones that don't are on hydrogen fuel cars as their only emission is water vapors.

aw89maxse, I completely agree with Jeff and Brian's ideas. They have put it most succinctly. Gas mileage isn't something you can pin down to just ONE cause. There are way too many variables. Look at all of them, fix what you can, and there is no way you will continue to get bad mileage.

For what it matters, during a cross-country drive this summer, my car got 30mpg on the hway, with me and about 300lbs of luggage packed in it.

 

i have a 89 max with 147,000 miles on it i put a cold air intake on it and took the muffler off and pit two 4 inch chrome tip's on it and i get around 450 miles to a tank of gas ......the other thinnk is i see a lot of post on no heat man mine will run you out after 5 mint of warm up time on it.....i feel for the one that dont get heat and no gas milage.....

 

yes thats a good way to look at it. I use to get 100 miles on the first and last 1/4 and like 125 on the middle 1/4 for a total of 450 a tank. Wow its been a long time sence Ive seen that. Now like 15 to 17 a gallon

 

I think I could get 300 if I tried, but it'd have to be a very judicious 300 miles. I would say I get about 260 miles on the average, with almost entirely in-town driving.

Then again, now that I think about it, my old VG-powered 87 SE 5-spd did the trip from the south Twin Cities area to Rockford, IL (approx. 360 miles) several times without ever stopping to top off. I would definitely peg my 93 Max SE as being more hoggish though.

 

......

 

I swear I made that post and I have no idea where it went.

I havent filled my tank up past the 1/2 way mark in quite a while, I need to fix the gas tank

 

Didn't you replace the o'ring already?

 

and just for the record
I sell gas tanks

 

Nope


infact I think I lost it

 

you deserved that

 

Dipshat. You need my spare again??