or if you know the percentage your speedo is off and calculate that into it. its not that hard really.

 

Ok, so if the exhaust doesn't have the faintest small of gas at idle, put it in neutral and smell for it running rich as someone else revs the engine. Also put your hand in front of the tailpipe to feel if there are any "pulses" in the exhaust. If a cylinder isn't firing right or has a significant problem you should be able to feel it in the exhaust every time that cylinder fires. If everything is good, it should feel like a steady, even, slightly vibrating stream of air.

Have you checked for a fuel line or gas tank leak yet? At 8 mpg I would really expect the exhaust to smell rich like gas. (Is there any chance someone else has been "using" your gas without you knowing? Reset the tripometer and put baby powder on the gas cap/cover to alert you to tampering).

If all of the above checks out ok, the next thing I'd do is pull the plugs and to see what they look like (take pictures and post them, nothing the cylinder numbers). While you're at it check that you have a clean air filter and a O2 sensor (check visually, are you running an oiled air filter?).

You can also take a multimeter and check the resistance of the spark plug wires while you're at it. Write down the resistance of each wire in Ohms and then divide that number by the length of the wire. They should all be within 5-10% of each other. If not, replace them.

Running low at idle is interesting. Sounds like there's a restriction somewhere (intake or exhaust), the ECU is getting a bad airflow reading, or you're getting incomplete combustion in a cylinder.

When is the last time the fuel and air filter were replaced?

 

Wait a minute, how many gallons are you putting in when you fill up?

(30 miles/day) x (3 days) / (8 miles /gallon) = 11.25 gallons

 

i think you arent calculating right, its the easiest thing in the world to do

i asked you for your stock tire side on the doorjamb placard so i can tell you the percentage to divide by? do you have 4.10s? what is your idle RPM?

 

my truck gets around 12 mpg in the city only because i have so much extra weight on it: 32's, steel wheels (5, if you count the spare in the bed) + the stock spare underneath! full brushguard, roll bar, receiver hitch, etc... weight plays a lot in what mileage your truck gets

 

WOW....don't be an *******. You never told us exactly HOW you were calculating it even though it was asked a couple times. As I said before, your speedo is off somewhere around 10%. I don't know exactly how far off it is because I don't know your stock tire size and your current size(33" you said).....figure out how far off you are, multiply that by trip meter at fill up, divide by gallons to fill, done. It's the most accurate you can get. It's stupid easy as hell. 08xlt4x4 is correct.



Did these problems all of a sudden start happening? Or you never checked mileage before? or....?

 

Agreed with Wannabe here. I'm not trying to sound like an ***, but from what I'm getting out of your posts this isn't something that all the sudden just started happening.

So quite frankly for you to get pissed at someone who gives you the methodology for actually calculating the MPG properly (your method seems a little bit sketchy) seems a bit rude your part. Don't bite the hand that feeds you so to speak.

 

maybe your neighbor is siphoning gas at night!

first off, do the proper calculation for you fuel economy so you have a solid starting point, including compensating for tire size. don't assume anything. don't get mad when someone is trying to help you, take the help gracefully.

if you don't know when the plugs were done, they're questionable at best. change them.

perhaps your fuel pump is on the way out. get the fuel pressure checked.