damn gas mileage!!!!!!!!!!!!!!

[fastpace]

well i was recently getting really bad gas mileage on my 240. Let me tell yall some of the history of the car:
1993 240sx
82xxx miles
regular maintaince
changed the fuel filter approximately 2,000 miles ago to 300zx fuel filter.
also changed the O2 sensor about 2,000 miles ago.

I usually check my mileage by filling up the tank, letting it go down to the halfway mark, multiplying the miles by 2 and then dividing by the capacity of the fuel tank(i just say 15). I checked my gas mileage about 3 weeks ago and calculated a 9.5 mpg. The car was idling really bad so I decided to check the spark plugs and that was one of the problems. So I changed the spark plugs and calculated my gas mileage to be 14.6 mpg. This is a big improvement from before, but still is not big enough. However, I do have a heavy foot. I haven't changed my spark plug wires yet, but I was wondering what are some other things that can be the problem?

[Dousan_PG]

timing?
maf?
air filter?
iiav?

any aftermarket modifications?

[fastpace]

nope, the only thing I have done was make a custom intake system. that is it. everything else is pretty much stock besides the fuel filter.

[mrmephistopheles]

Heavy foot = **** for gas mileage.
I suggest going easy on it (shifting before 3k) for a full tank and see what happens. That'll give you a much better idea on how fuel efficient your car can be. Also, try to limit the amount of times you start the motor. Do this and then we'll be able to figure out whether or not your motor is performing poorly.

[fastpace]

thanks for the advice i will try that my next fill up. almost every gear when I get carried away is at the 6k mark.

[kalieaire]

search for "power balance test". you'll see several posts by me.

use that to determine which cylinder(s) is(are) causing problems.

if i'm right, it's probably a leaky injector.

[Cheng]

I'm just curious of all you 240sx with the sr20 swap. Intake, exhaust, stright pipe, fm/ic, BOV, downpipe, upgraded fuel pump, and running at 10psi what are you gas mileage. Because on a 12.2 - 12.5 galloon of gas I would get about 210-220 miles for the tank, so that comes out to a little less then 18mpg. That is a little of highway driving, and some times i have a heavy foot so 1st and 2nd gear i don't shift till 5k or 6k and then from there on usually 3500 to 4500. But my normal driving shift point is about 3k to 3500.

[kalieaire]

i driven badly on a tank before, ~23 mpg, i've driven nice on a tank before ~24mpg.

i'm supposed to be ~30-32 mpg.

------------if you have an sr, you should be ~24-26mpg depending on what the condition of your engine is.

I think that you should all take that mileage rating as a goal to reach for. Since you know that all your engines are old and such, you can slowly begin to recondition the engine to the point that it's close to new condition and work as well.

[Cheng]

Yea, but are you doing highway driving or street driving, because it makes a big difference. On the SR mix with a litte of both I've hit 245-250 before and thats also with about 12 galloons. and thats only about 21 mgh.

[kalieaire]

my friends hit over 300.

[Cheng]

How on a s13 not s14, because s14 has a bigger tank. If its a s13 is he running with sterorides

[Got Sileighty?]

i usually shift at 2500....yea yea yea im cheap on gas hahaha....but i think im getting about 20-21mpg. isnt that still crappy?? i usually do city driving, but with my granny-style driving, shouldnt i be getting more?

the way i calculate is i wait til gas light comes on. put $5 of gas ~ 2.5 gallons. then i calculate miles i get until light comes on again. which is about 50-55 miles.

[Cheng]

That sounds more like the numbers im getting, even with the stock KA i was getting like 18 or 19mpg which sucks. But does anyones else has numbers out there.

[fastpace]

well this is an update on the gas mileage. well I wanted to thank everybody for their advice. On a half tank of gas I recorded 140 miles and that equates to about 18mpg. I did however go crazy a couple of times, but for the most part I shifted at about 3k rpm. But I am going to see what other things I can do to improve my gas mileage. Does anybody have any other ideals of what I can do?

[kalieaire]

Originally posted by fastpace
well this is an update on the gas mileage. well I wanted to thank everybody for their advice. On a half tank of gas I recorded 140 miles and that equates to about 18mpg. I did however go crazy a couple of times, but for the most part I shifted at about 3k rpm. But I am going to see what other things I can do to improve my gas mileage. Does anybody have any other ideals of what I can do?

I have a GREAT idea. Why don't you first follow our previous suggestions first?

[Steeles]

my setup
96 blacktop S13 Sr
14.5psi
FMIC
greddy intake mani
FMIC
4.36 final gear (so mines low)

but I got like 368 miles out of something like 14.xx gallons of gas

[Red]

Well when I replced my old plug wires and fuel filter my gas mileage went up. If I drive with the AC on the whole time I get 240 miles on 12gal If I drive with it off I'm pushing 290gal.... 275 if I get on it a few times messin with the civics. :) not to bad... When I 1st got the car I would be lucky to get 170 miles in 12gal (that was befor I replaced almost everything to do with fuel)

Spark Plugs, O2's, Fuel filter, Plug wires, Distrubiter and cap(spellin)

Next is, Injectors, Fuel pump, add/replce a FPR, hack the maf and maby get a bigger fuel filter like a 300zx one.

EDIT: forgot some junk

[twitchy]

i went 200 kms this weekend and burned half a tank of fuel..this was all highway. Im takin it in to get it checked..thats insane. I was cruisin with mustang GT's and even a camaro this time with a 350 and they all got way way better mileage than I did

[Cheng]

yea i think our gas mileage is around 17-20 on stop and go driving. It also vary a lot from stop and go driving to highway driving. This weekend all i did was drive on the freeway i got about 150 at half tank(Full tank im guessing 290-300), and usually at half tank i get maybe 100(full tank i usually get about 210) for stop and go driving. Look at the difference between the 2 numbers.

[Bbandit]

take it easy on the gas pedal man :D

i went to san antonio last friday and for the whole trip, i used only half of my gas tank
but i was going at 45-55 mph average at 5th gear.. haha

[misnomer]

You guys missed a MAJOR point of error here.

Fastpace: You are measuring your mileage by how far you go when your tank drops to 1/2. Bad juju. The gas gauge is an estimate at best. What you need to do is fill your tank, drive it to half or more (the more you drive, the more accurate your calculation), and then fill it up again. Take the number of miles you drove, divide by how much gas you just bought. That is an exact measurement.

As far as improving gas mileage goes, it is typically more driving style as condition of your car. RPMs aren't the best way to regulate, as you can still burn a lot of fuel if you floor it to 3k. The more open the throttle, the more air gets in the engine, the more gas is used. Slow down to save gas. Most importantly, calculate your mileage correctly, and then let us know how bad it is. Depending on your city/highway driving, I'd expect between 24 and 32 on a KA (I've measure the full range on my '92).

[Got Sileighty?]

whoa! thanks misnomer. thats what ill do next time. i think im in for some bad news though cuz im pretty sure my mpg just got worse this week. i had to use a/c for like 3 days (total of 30mins, about 10mins each way). i had just put in about 2.5 gallons 5 days ago, i went about 40miles and its empty again. so thats about 16mpg, and i only used the a/c for those 3 days. wtf?

could it be that i had just replaced the fuel filter a week and a half ago?

[mrmephistopheles]

I guess you just skipped over my post... :(

[Cheng]

Well thats what i do an i still get about 17-20 mpg

[misnomer]

mrm: I read your post, but figgered given his current method he would have guessed the full tank size rather than the actual amount of gas he would refill it with. I knew what you were thinking, just clarified without giving credit :)

[fastpace]

thanks for the advice, i might of missed that info somewhere. I will do this when I fill up.

[kalieaire]

Originally posted by misnomer
You guys missed a MAJOR point of error here.

Fastpace: You are measuring your mileage by how far you go when your tank drops to 1/2. Bad juju. The gas gauge is an estimate at best. What you need to do is fill your tank, drive it to half or more (the more you drive, the more accurate your calculation), and then fill it up again. Take the number of miles you drove, divide by how much gas you just bought. That is an exact measurement.

it also helps to keep experimental error down by using the same pump from the same station. that's how i get such consistent readings.

[ItzGenX]

My gas mileage on my 95' SE with KA (Intake,Headers,Exhaust) gets 390 miles per 13.4 gallons. I used to only get 300, but I changed the spark plugs, did an oil change with engine restore (works-i have 140k miles) cleaned my air filter and added redline injector cleaner in the gas tank (works too). How I check my mileage is when I pump a full tank, I reset the trip odo until I pump again *usually on E*. When I pump again, I look at the gas pump to see how many gallons I pumped to get it full and divide that into my trip miles to get my average mileage (I have a heavy foot). The gas guage is however an estimate like someone posted because when I am on 'E' and pump, I can only squeeze 12.9-13.7 gals in there.

[Jeff240sx]

Bah. I don't see how you could even think about guessing mileage based on the gauge showing 1/2 tank.
All cars have a certain ammount of falseness during their first 1/4 tank or so. The needle will deflect less than the ammount of gas you actually used. This is so when you test drive a car, you can drive for damn-near ever, and then the car salesman points to the gauge and says "Look, you've gone 50 miles and the needle hasn't moved. How's that for gas mileage?!" It's all a plot, because after that, the needle moves faster than it should, to make up for the first 1/4s deflection error.
-Jeff

[fastpace]

just a quick update(again): filled up the tank today and here are the readings:
176.7miles/9.165gallons= 19.28mpg

thanks for the advice again, it is even better than I thought before.

[RedlineRacer]

I usually only put in half a tank (6 gallons cause it is around 10 dollars) everytime I got to the gas station cause I am a cheap bastard. I can usually get 150-170 miles out of that if I drive conservatively.

[Bill Roberts]

16.1 Gallons. Top miles, 403.7. Gas can in back. I ran out. Dont poo poo running out. My tank is pristene and no trash.

Interstate driving at 70-80MPH. 5th gear, very little hills, no sudden acceleration.


Normal driving, and spirit driving, normal 240SX driving.

283.4 miles @ 16.1 gallons to dead.

Racing in closed course oval for hours at top speed and d shifts. Tach running 6 to 7 continuously.

128.9 Miles 16.1 gal.

Ok lets take this to top, normal, worst.

25.07MPG
17.6MPG
8.0MPG


Do the math.


Top speed is 137 to 141MPH course lap...very top is 147. Not fun above 135MPH

This is with a modded KAE running >200HP N/A

[higatsuku]

Another factor you may want to take into account is the octane of the fuel. I was using 87 for a while and my gas milage was terrible. I've recently been using 93 octane and it has done wonders for my fuel economy. It costs a little more, but its worth it.

[Bill Roberts]

Depending on your compression ...agreed.


Cars running less than 9 to 1 and properly timed. it will make no difference at all.


If you have 10 to 1 or better, you will get better mileage out of ethyl (old school name for high test...or 92/3 octane)


If you are 9to1 and ethyl gives you better mileage, your timing is off a shade.

[mrmephistopheles]

my .02 pesos:
I have a stock KA24DE (exhaust only).
I run '87 like it's going out of style.
I've gotten over 450 miles out of a tank and over 31mpg in highway driving.
I've also gotten less than 200 miles in spirited driving.

Bill, how are you getting a 16.1gal tank? S13 is 15.9.