Why am I getting 11.5 MPG on the interstate?

The Green GT · Apr 24, 2007

I know I just put gears in, but even the 15 I was getting before that is horrible. I cant see why I get 11 MPG on the INTERSTATE. I am usually going around 75, but I hit 80 every once in a while. Ill go faster when Im passing someone. But since I noticed my horrible fuel economy, I dont really bother anymore.

New O2 sensors, cleaned MAF a few weeks ago, tuned up less than two years ago. Could use a tuneup I guess.

So what should I look into? Maybe the timing has something to do with it? I wouldnt think it would make my MPG THAT bad though.

JJ95GTID · Apr 24, 2007

There is definately something wrong there.
I can get 23mpg but average around 20mpg.
Worst is 17mpg which happens in the winter when I let the car warm up idling.

trav_19 · Apr 24, 2007

yeah my 94 is running a 20mpg easily....hmmm is it running rough at all?? did you ever put mufflers back on your car? maybe not having the back pressure is really hurting you...

Therian · Apr 24, 2007

running an EGR still?

STM1965 · Apr 24, 2007

I'm getting just over 17 and that in the city. Oddly enough its about the same millage I'm getting with my 04 Honda Oddessy. So the family funster is parked and I get to drive the toy more

The Green GT · Apr 24, 2007

EGR still there

Mufflers on

Runs and idles perfect.

wlink1 · Apr 24, 2007

Maybe try and replace the fuel filter

The Green GT · Apr 24, 2007

I changed that this year. So its not old at all.

Therian · Apr 24, 2007

when was the last time you cleaned the air filter?

The Green GT · Apr 24, 2007

I installed a CAI less than a year ago. But I guess it could use a cleaning.

Therian · Apr 24, 2007

air filter is usually the #1 cause of bad mileage...also make sure you have your tire pressure correct.

Is there any chance you are leaking fuel anywhere? do you smell gas at all (more than normal?)

BlownFiveLiter · Apr 24, 2007

Do you have any codes? I use my car to commute on occasion, and in all stop and go traffic, I'm pulling down 16-18mpg city. I haven't even checked my highway mileage, but I'm sure it'd be better.

The Green GT · Apr 24, 2007

Therian said:
air filter is usually the #1 cause of bad mileage...also make sure you have your tire pressure correct.

Is there any chance you are leaking fuel anywhere? do you smell gas at all (more than normal?)

Ill check the filter later. And I check the tires regularly. I set them right not long ago. And I have an O/R H-pipe. I always smell gas lol. But its always burnt. I never smell raw gas.

StangGT1995 said:
Do you have any codes? I use my car to commute on occasion, and in all stop and go traffic, I'm pulling down 16-18mpg city. I haven't even checked my highway mileage, but I'm sure it'd be better.

Last time I check ed codes I got nothing. And I was getting the bad MPG then too. But Ill do it again.

final5-0 · Apr 24, 2007

You said you just done some gears

Maybe your speedo is hosed and throwing off your miles driven

Grady

The Green GT · Apr 24, 2007

final5-0 said:
You said you just done some gears

Maybe your speedo is hosed and throwing off your miles driven

Grady

My odometer doesnt even work. I checked the distance in my sisters car. Ive been riding to school with her in an effort to save $$. lol

And do gears throw off the odometer even if you have the right speedo gear?

wlink1 · Apr 24, 2007

With the correct speedo gear your odometer should be correct.

Not sure if you have tried any injector cleaner, I have had good luck with the lucas, I ran that in my wife's trailblazer before our trip to florida and loaded down with a/c on and the 5.3L we got 25 miles to the gallon which was a couple mpg better than normal. Also when was the last oil change? That could affect mpg

The Green GT said:
My odometer doesnt even work. I checked the distance in my sisters car. Ive been riding to school with her in an effort to save $$. lol

And do gears throw off the odometer even if you have the right speedo gear?

sage2k · Apr 24, 2007

its hard to calcuate how your gas milage is without an odometer
but anyways
back when i was making like 8$ an hour and could barely afford gas I would drive 60mph on the interstate and pull over 20mpg
I drop an easy 5mpg by driving at 70mph

final5-0 · Apr 24, 2007

sage2k said:
its hard to calcuate how your gas milage is without an odometer
but anyways
back when i was making like 8$ an hour and could barely afford gas I would drive 60mph on the interstate and pull over 20mpg
I drop an easy 5mpg by driving at 70mph

I agree

To be the most accurate you gotta:

Fill up on level ground and get all in the tank you can
Write down the mileage at fill up
Drive until the tank is close to empty
Fill up exactly as before
Write down the mileage
Divide the miles driven by the gallons used

Very simple ... yet ... Very effective

Guessing about mileage or gallons used is just that ... Guessing

Grady

95five-oh · Apr 24, 2007

i get about 16ish in mine driving about 60/40 highway/backroads on stock 3.08s... driving pretty conservatively. u guys that are running over 20mpg on a consistent basis must all have 2.73s and spend 90% of your time on the interstate, i hardly ever break 200 miles on a full tank.

mo_dingo · Apr 24, 2007

I would check all the spark plugs and make sure every cylinder is firing clean. A cylinder balance test may lead you to a problem too.
Scott

Why am I getting 11.5 MPG on the interstate?

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