ve is a 99 nissan altima. It's a 4 speed automatic and the overdrive gear activates at 37mph and goes all the way to 100+ I can't seem to break 26mpg. Here are some things I changed. ...
 

The car I have is a 99 nissan altima. It's a 4 speed automatic and the overdrive gear activates at 37mph and goes all the way to 100+

I can't seem to break 26mpg. Here are some things I changed.

1) Kumho tires at 35 front, 33 rear
2)Transmission cooler( it works because it gets hot after driving for some time)
3) Higher bar radiator cap which means the coolant can obtain a higher temperature without over heating the car.
4) Spare and jack removed.
5) Royal purple synthetic engine oil
6) Use NGK V power copper spark plugs
7) Use AC only when it's really hot outside, besides that it's never used.

I drive 55mph on the freeway and my consumption went down, I try to coast as much as I can on the freeway and on the streets. I use cruise control all the time. My driving is usually 55% freeway and 45% streets.

Now before I started doing all this my mpg for the whole tank was 24mpg. Now it's 26mpg, but I can't break the 26mpg barrier. Any advice???

Also nothing is broken on the car, everything works.

I used to have a complete MSD system: Box, coil, tach adapter. But the mileage is the same between stock and msd system.

I'm doing everything I can but I want to go over 26mpg and even want to hit 28mpg if possible.

I've heard that msd
 

I've heard that msd ignitions don't do crap, if you look for my post about engine management it'll say why.

In any case, try some acetone or something, there's lots of small stuff, you tires aren't pumped up very high, and most performance tires can usually be pumped up to 51 psi, but I dunno about yours.

I'll think about this some more now.

Re: I've heard that msd
 

For the freeway I see some use for pumped up tires, but for the street would more psi hurt because the car accelarates and there is more weight in the tires?

More air in the tires for
 

More air in the tires for acceleration will be a miniscule difference in inertia, even under that most stop and go you'd still be better off pumped up.

PS: Nice to see you here, I'm working on an ecu now, but later I'll get around with some nicer tips.

Re: More air in the tires for
 

Ok I'll wait on those tips.

26 mpg seems pretty normal
 

26 mpg seems pretty normal for your car, but who the hell wants normal!? 40 mpg would be sweet, but hard to achieve, but possibly possible, I think.

Things to try:
acetone 1-3 ozs (testing)
modifying your spark plugs (look for the thread I made on it, more power without fuel consumption increase means less need to punch the gas all the time)
any of the random many fuel additive out there (poke about for some)
fuel vaporizations device (not as good as on carbed cars though)
mothballs in the tank (crushed)
45 psi in your tires
Check your 02 sensor to see if it's not looking good, might need replacing

More to come...must shower now (still soldering anyway).

The first thing to do is to
 

The first thing to do is to avoid most of the gadgets out there. The purpose of this site is not only to discuss possible solutions to increase gas mileage, but to back it with data.

Since your car is a 99 I doubt your O2 sensor needs replacing. I just replaced mine in my 89 Civic and the original one was still there. Hell, it didn't even need to be replaced. I just did it to do it.

Another easy thing to do is to make sure your car is clean. Make sure the cap/rotor on your distributor is clean and that your wires and plugs are in good shape. You can always test your wires with a multi-meter.

have you replaced your fuel filter recently? It's never a bad idea to do so. There are a few articles on this website that have simple tips for making your car more efficient.

I owned a 2001 Sentra (manual transmission) for a few years until I was on the receiving end of a hit and run last year. it got around 26mpg. The Altima is a much bigger car than the Sentra, and I believe the engine is larger too. You're still getting better mileage than I was. I'd be curious to know what the EPA rating is for your car.

Lastly, welcome to the board!

The fuel filter is clean.
 

The fuel filter is clean. The EPA rating is 22 city/ 30 hwy.

The motor is 2.4 Liter it goes dead rich at 3000rpm.

At 55mph I'm at 1800rpm
At 60mph I'm at 2000rpm
At 65mph I'm at 2125rpm

My best results so far is 55mph.

That's pretty tall gearing
 

That's pretty tall gearing for an auto, mine is 3k rpm at 65 mph.

Hmm, 2.4 liter is a lot of displacement, I'm right to assume 4 cylinder though?

You could try a warm air intake.

Re: That's pretty tall gearing
 

yes 4 cylender. I actually did buy an Injen WAI( warm air intake) but all it did was make loud noise and killed my low end. I took it off and put the stock intake back.

Sounds about right, haha.
 

Sounds about right, haha. Ever think about patching up the underside of your car to reduce drag?

Re: Sounds about right, haha.
 

What can I use and does anybody have any pictures as a reference. Btw, the ground clearance is 6 inches.

You can use some really
 

You can use some really tough plastic or aluminum. Just get under there and look for all the not flat places and cover them up. You just use self tapping screws (they drill their own holes) and whack them in there. Just make sure you treat the areas with some junk to keep water from getting all over the screw holes.

How much of an increase can
 

How much of an increase can I expect in mpg from making the bottom of the car flow more?

Also any other advice that I can do that is cheap or free?

And why is it better to be at 2800-3200 rpm to receive better fuel economy when mine is at 1800 for better fuel economy. I notice civics drive at 3000rpm on the freeway and receive great fuel economy, while if I drive at 3000rpm it would waste a lot of gas.

Just Rented an Altima -- Backpressure?
 

I just got back from a trip and rented an '05 Altima 2.5S. This thing had gobs of torque -- I'm told that the reason is the muffler (with a spring-loaded valve that holds back-pressure until higher RPMs release the valve to improve high-end). If your model has the same muffler, maybe there's too much backpressure? Honestly I chirped the tires accidentally several times -- much more exciting that the Buicks they usually stick me with. I ended up with 21 mpg with mostly city driving and being in a hurry most of the time.

Anyways, check your tire pressure and stay at or above 40 pounds. Perhaps a different muffler with more free-flow could improve cruising (so the engine is not working so hard to push out that exhaust). Maybe I'm way off here...someone back me up on this (or disprove it, I don't mind).

-RH77

My 1.5 liter can go 3k and
 

My 1.5 liter can go 3k and getter much better mileage than your 2.4 liter just because it makes less power. Simple as that, plus it weighs less and blah blah blah. I dunno to be honest how much the decreased drag will help. Ernie Rogers on here has done some crazy drag stuff and gained a ton, but he had this huge wing too, this is something I plan on testing down the road.

Re: My 1.5 liter can go 3k and
 

He hit the nail on the head with ths one. The difference between your engine and my engine is the size. When I had my wrangler I had a ridiculously low idle, but I also had a 6 cylinder 4.0 Liter engine. I averaged 15 miles per gallon. I remember when I drove to Vegas from Southern California how excited I was to get 20 mpg. I definately don't miss that brick.

Honda's major MPG advantage has been their desire to stay with the smaller engines. Even their newest engine is a 1.8L which gets the fuel economy of a 1.5 and the power of a 2.0. I think Honda realized a long time ago that if people REALLY want power they will drop the engine in themselves. So far that is true.

If you are really serious about fuel economy you'll switch to a smaller engine/car. My 1989 four door sedan gets high 30's (maybe 36-38 mpg) in city driving (well, it used to before I had some engine problems). I'm certain I can get my car above 50mpg with a combination of proper driving, a new engine, a new transmission, and the new tires I plan on getting sometime soon.

So start small. The next time you get tires, spend the extra $10 per tire and get the tires with "Low Rolling Resistance." you'll probably notice a 3-4 mpg boost right away.

The tires I got right now
 

The tires I got right now are new. They are only 5k old. They perform better and they have a better grip in the rain.

I wanted to get the 06 civic with the new 1.8 liter which gets high 30's. They are lying about the power, it's actually more like 150-155hp I think they are saying it's lower for the insurance companies.

I'm really not going to get a different car so I can increase my mileage by 10mpg. I spend a boat load on this one and plan to keep it until I finish college or save up money. I just fixed the rust in the engine bay, changed the drivers door locks/window box, put newer hubcaps, paid for new registration.

My mom has the 2.5 altima, the car accelarates like a raped ape. If you put it manumatic mode be prepared to be pushed in the seat really hard. First 2 gears are REALLY torqey. The 2.5 altima is the crapiest car we ever owned. So far engine broke down 2 times and now we got a problem where there is loss of power at 3k+ and the dealer can't figure it out.

Haha, very interesting cars,
 

Haha, very interesting cars, these new cars. Sometimes I am tempted just to get some random dohc honda engine, turbo it, and drop it in, and I could still get 40 mpg driving conservatively and around 200 hp, but these new cars, meh. I spend less than half a percent of my time driving about 3k.

In my car I rarely see
 

In my car I rarely see 2500rpm, it runs very rich.

Any more tips guys?

I'm actually curious to know
 

I'm actually curious to know what your driving habits are like. Do you drive mainly for commuting? Running errands? All City? Freeway?

Another possibility is to look into a Warm Air Intake. I am planning on comparing a warm air intake to a cold air intake sometime in the next few months. The theory is that warm air (usually drawn from your exhaust manifold or cat) helps somehow so that your gas/air mixture is more lean.

I have already tried a warm
 

I have already tried a warm air intake. All it did was groan, and killed my low end.

After 2500 it set apart from the stock intake. From 2500 to 4000rpm it made the car a little faster.

I actually had a a/f gauge when I had the intake and I ran 1 bar richer. It made the car run richer.

The msd ignition didn't help either. It killed my top end. I have very little of it anyway but at 2750 is when the MSD really made the motor pick up.

The only thing I believe which helps me in the long run is my 1.2 bar radiator cap. The original radiador cap was 0.9 bar. The higher the bar the more times it takes for the motor to heat up. The more bar it is the hotter a motor can run safely. Meaning If I drive for a long period of time I will achieve better and better fuel mileage as I go. The only negative effect of this is it takes a longer time for the motor to heat up, killing my gas mileage. It takes 1 minute of warming car and driving 4-5 miles to go to close loop. As soon as the car goes in close loop the overdrive gear engages.

My driving habits are accelarate light( making the auto shift at about 1700 in every gear). If I see a red light ahead of me I coast to it. I do a lot of coasting. On the freeway I drive 55mph on cruise control to get good gas mileage. On the streets I drive the speed limit because my overdrive activates at 37mph so I usually drive 40mph on the street. I rarely have cruise control on the street because it's go and stop traffic.

I drive about 60% hwy and 40% city. I drive to school, work and to meet my cousin. At my cousin's we either take his car or my car, we switch back and forth like carpooling. We go to clubs, friends, and etc. Even with him I try to drive 55mph with cruise control.

Judging by rh77's recent
 

Nevermind!

Re: Judging by rh77's recent
 

What you mean?? Were you going to say something?

Haha, yes, I was thinking
 

Haha, yes, I was thinking since rh77 went from 26 to 31 with his warm air intake...and I posted something about it, then I looked up, and thought, oh yeah, I remember now, but of course I can't delete my post.

oh ok. Well different motors
 

oh ok. Well different motors work different when mods are applied to them. I know for my engine If i were to get a header my mpg would go up to 28mpg without driving like a grandma. A header is $400 so that idea is out.

You might want to try and
 

You might want to try and air damn, especially seeing as it is winter time now, I'm about to post on it.

Royal Purple FYI
 

I tried Royal Purple 5w30 in my 89 Chevy Celebrity 2.8L V6
MPG's went DOWN ONE MPG on average - 3000 mile run

Tried Royal Purple 10w30 in my 93 Geo Prizm 1.6L 4cyl
MPG's went down TWO MPG's on average. - about 2500 mile run

Went BACK to Mobil One. Mileage went back up too ;)

AND tried NGK V-Power in my 2.8L V6 - worst plug I ever used!(NO POWER, 8MPG DROP, and just didn't run right! used these for ONE tank of gas, then ousted them)
So I'd suggest a platinum NGK. I used G-POWER NGK's to REPLACE the copper bosch's in my 94 3.4L DOHC V6 and I Raised the average MPG by 4mpg!!! (and its higher than EPA's rating of 26mpg all highway (at 26.67mpg with 70% highway driving now)

...however your engine is a lot newer AND its OBDII so who knows
~Will

Re: The fuel filter is clean.
 

...and you say that it goes dead rich at 3000rpm...what if you hold it there, it should fluctuate if the o2 is healthy.

Your o2's are expensive for that motor, in the sixty dollar range for each...
call some shops, and see if a tech will examine the o2's operation...
maybe a modest price of $30 for the exam?
some o2's will get SLUGGISH and thats what will hurt your city mpg's...thats what the exam will determine. And make sure you ask using the words "sluggish"...
~Will


The motor is 2.4 Liter it goes dead rich at 3000rpm.

Hell, just pull the o2 and
 

Hell, just pull the o2 and look at it and see if it looks like crap. 60 bucks ain't really terrible for an o2, of course my car will take a 17 dollar o2, but it's a piece of crap, I'd gladly pay 60 to get the one I wish I was running, :-), might be worth trying swapping them, mehbe your cat is bad or junked up? You can always pull an 02 from the junkyard and swap it and see if there's a difference.

Re: Hell, just pull the o2 and
 

The cheapest I can find my o2 is $180. Honda sells them for over $300.

Anyway, SVOBoy makes a good point about the CAT. I had a 2000 V6 Jeep Wrangler that I drove for a little over a year. It was horrible going up hills (I'm speaking of Parley's Summit near Park City, UT). I can understand a 4 cylinder having problems with that route, but not a v6 Jeep.

Then my friend told me that his friend's jeep did the exact same thing. It turned out that the CAT/exhaust was clogged. It was creating extra back pressure and bogging the engine down.

i'd check the CAT personally.

It goes rich not because of
 

It goes rich not because of the o2 sensor but because of the ECU. It's common on nissans. NGK coppers actually improved my mileage because platinum is made for longer life.

I have never got my mileage this high under platinum plugs. I got the same 28.7mpg but that was all freeway. This 28.7mpg that I got yesterday was 60% freeway and 40% city. So the mileage increased.

The only difference I made was switching to copper plugs and switching to royal purple. So they work for me.

Try gapping/modifying your
 

Try gapping/modifying your plugs, see if that helps. You could always get a piggy back sensor to keep the ecu from maxing out fuel injection.

I got some more stuff in my
 

I got some more stuff in my mind that can increase fuel economy. The ecu only starts going rich around 3000rpm. On the streets i'm below 2000 and on the freeway below 2500rpm.