Im getting around 200 miles to a tank on my 96 f150 with the 4.9 i6. I recently changed the fuel filter and spark plugs. If my math is right, thats about 10mpg. I use safeway 89.

It see’s city driving, but not stop and go. Ive used lucas oil fuel conditioner but im still getting IMO bad mpg. I dont floor it and i dont tow anything.

wondering if someone can point me in the right direction for things to check, and possibly replace? I know this truck can do better than 10mpg lol..

 

My 4.9 will use around 17 gallons every 225 miles. My fuel gauge is erratic, so I have been resetting the trip meter and filling up at 225 for years. Almost always within 1/2 MPG, depending on where I drive.

That averages out to 13.3.

 

My 1990 300 6 cyl. with a 5 spd. manual and 4WD (std. cab, 8 ft bed) got 17 to 18 mpg on the highway.

10 or 12 would be pretty bad. Got to be a reason it's drinking gas like that. No idea what it might be though.

Good luck with it. Great trucks and that engine can last for a long time (251,000 on mine when I traded it in and my cousin's 92 has right at 340,000 on the same engine/truck style with a 4 spd. manual).

 

Your truck is EFI so there is not much you can do as the computer is controlling the fuel but ........

Is the check engine light (CEL) on? Dose it even light up when you first turn the key on like the other wornning lights do?
If no CEL in the dash I would pull codes to see what the computer is saying as there has to be something off.
It only takes 1 sensor to be bad to put the system in "limp home mode" and this will make it run rich and lack power.

Also you cant say "getting about 220 miles to a tank as that dose not mean anything.
You need to fill the tank(s) and take down the mileage.
Then re-fill the tank(s) and mileage again and the gallons it took to fill up.
Do this a few times so you know they are about the same on each fill up / mileage / gallons.

Subtract the last mileage from the first mileage and you have a total of miles for that tank.
Then divide the miles by the gallons and that will give you your MPG
Say you went 350.3 miles and it took 21.6 gallons 350.3 / 21.6 = 16.22 MPG

Now before you go doing that you need to make sure your speedo / mileage is on the money.
To check the mileage find mile posts on the high way and check it between markers, do 2 or 3 of them to make sure it is reading right.
Different size tires other than what the factory installed can throw off the speedo / mileage readings and this needs to be on the money to get the right MPG readings.

BTW my 81 F100 flare side with a 300 six / NP435 w/over drive / 2.75 rear gear and factory size tires is only getting high 14's to low 15's MPG.
That is a combo of high way to work (65 - 70 mph) and back roads home (45-50 mph with a few stop lights).
I Have a air fuel. ratio gauge installed and have been working on timing and carb setting (its rich) to get more MPG.

My 02 Durango 5.9 EFI / auto trans 3.92 rear gear is only getting mid 15's on the same roads.
Dave ----

 

What size tires do you have?
What is your gearing?
What transmission?


Things to check:

As mentioned above, make sure your speedometer is correct. If you have a phone, there's a lot of free GPS apps that'll tell you your speed.
A clogged catalytic converter (lots of exhaust shops will check this for free)
Sticking e-brake. The brake line can get rusted in the sleeve and make the rear brakes drag.
Sticking brake calipers. Old calipers, or those in need of maintenance, can stick, and cause the front brakes to drag.
Is it in need of a tuneup? How old are the spark plugs? Cap? Rotor? Have you checked the base timing?
How old are the fluids in the transmission and differentials?

All of that stuff can add up and cause the engine to work harder than it needs to be to maintain speed.

 

i did the math on the miles per tank, thats how i ended up with my mpg. thank you for your input, ill be scanning today to see if anything pops up.

i am unsure of my gearing, but i have the 5 speed 4x4, i believe it is the MD05(?) I have 31.5" tires, my plugs look fine they are brand new. i do have an issue with my ebrake NOT wanting to engage about half the time i try to use it, so maybe that is actually causing it to stick at times? the light turns off but maybe its still sticking. i need to learn how to check the rotor and cap to know what is acceptable and what will casue a bad spark, if thats what would be the problem. i dont know how to check the base timing yet. i have no idea on the age of the transmission/diff/transfercase fluids but they are on my immediate replace list.

 

well here are the codes currently. I will google later to understand them

 

It looks like you have some work to do to fix them codes then the MPG may get better.

Again doing the math per tank and not doing the mileage & gallons is just a guess at best.
Also the 31.5" tires I dont think were factory were they?
If not then your readings & math will be off.

I hate to be that way but its the only way to get the right MPG reading.
Dave ----

 

I would guess on a plugged cat with those 4 codes all together.

The 31 tires aren't going to help mileage either.

These trucks came with 235/75/15 tires. I have 30/9.50/15 on mine, which is one size above factory in height, and pretty much factory width. According to two GPS units, this has my speedometer right on the speed and stated mileage the odometer reads.

 

yes, i went 197 miles on 18.6 gallons of fuel. Thats 10.5 mpg unless im smoking the strong stuff. The tires are taller than the OE ones. I knew that would impact mpg but not like this. Your saying my numbers are basically useless now that i have new tires? I was under the impression the 4.9 would do around 14-15mpg city, i didnt think these tires would drop it that low, barring nothing else impacting engine efficiency.

do these trucks have one or two cats? Im pretty sure my cat has been removed. I will double check tomorrow in the light. I know previous owner deleted the exhaust component under the bed with a straight pipe.

 

What I meant was if going by the mileage on the gauge it is not right with the 31.5" tires, just like the speed reading being off.

Lets see if I get this right so bear with me.
You have a taller tire on the truck, IIRC it will slow the speedo & less mileage for the speed & miles driven.
You may show say 50 MPH but you are only doing 45 MPH and for every mile driven may only show say .75 miles on the gauge.
Again I am only using the numbers to show what could be happening and why you need to make sure the speed & mileage on the gauge is what you are doing.

Your 197 miles may be say 230 miles on the 18.6 gallons. that would be only 12.37 MPG (230 / 18.6 = 12.365) still not good but better than the 10.5 you got.
So you need to check the gauge to make sure it is right and get them codes fixed.

As for the 14 - 15 MPG in the city dream on, I can just get 15 MPG doing high way 70 MPH and back roads at 45 to 50 MPH and I dont have a 4x4.
Do you have a tach in the truck and if so when on the high way what is it reading and at what speed?
It could be you are way below the motors sweet spot, I want to say mine is around 1800 RPM or a little more.
Dave ----

 

Check for a dragging brake - with an infrared gun or use your hand to touch each wheel for heat.

 

I would think if a brake was dragging to hurt MPG that much it would be smoking from all the heat!
But thats me
Dave ----

 

I was just surmising based on what I found on a car trailer once.
Or maybe all four are dragging just a leedle bit?

 

Hey Subzerospeed,,,
As I read all your posts it is hard for me to figure why someone would be asking about bad mileage WHEN you pretty much have your own answers.
Looks like You need to spend more time checking what you have and fixing problems BEFORE asking questions.
These guys on here are a GREAT source of information BUT it is hard for them to answer questions when you have not done your homework first. (how many converters on my truck) get under there and look.
You have codes up the _____ and not sure of your mileage and asking these guys on here why you have bad mileage???
I think everyone here is always willing to give great advice but we probably should help ourselves first.
Have all codes cleaned up, know exactly your mileage, then if your gas mileage is what you think is bad ask for input and ideas. You will then receive excellent ideas of what the problem may be.....
My .02 worth..