f150 5.4 mpg question

[7 point]

I have a 04 f150 5.4 it always got good mpg like around 16-17 city but in the last year it's been getting between 13-17 I'm driving the same and going the way I was before it stil runs and drives good no loss of power I haven't done any mods .anyone on here run in to the same issue?

 

[model88_308]

I have the exact same truck. I noticed a difference like that (but at HWY) after a tire change. I cured it. I rarely bother checking it any more.

Also, gas with ethanol vs gas without WILL cause that exact phenomenon.

 

[7 point]

Do you have stock size tires on it

 

[model88_308]

Do you have stock size tires on it

I put larger than stock on it, mileage dropped. I now have tires in between stock and the previous size (305/70/17s)

 

[Mr Bya Lungshot]

I have a 04 f150 5.4 it always got good mpg like around 16-17 city but in the last year it's been getting between 13-17 I'm driving the same and going the way I was before it stil runs and drives good no loss of power I haven't done any mods .anyone on here run in to the same issue?

Did you ever replace the spark plugs?
How many miles do you get out of a full tank and how many gallons is your tank?

 

[transfixer]

I have a 04 f150 5.4 it always got good mpg like around 16-17 city but in the last year it's been getting between 13-17 I'm driving the same and going the way I was before it stil runs and drives good no loss of power I haven't done any mods .anyone on here run in to the same issue?

I don't have that truck, but because of some fellow automotive techs I'm familiar with the weak points of that engine, it could be your cam phasers have worn out/are wearing out, they're hydraulically operated , and affected by dirty oil also, they are controlled by the computer to adjust the timing , when they wear out you usually hear some noise from the top of the engine, and your timing won't be what it should be, which can drastically change your fuel mileage. Worn oil pumps also contribute to Cam phasers not working right.

 

[7 point]

The truck only has 59k miles it has a little bigger than stock tire size 265/70-17.

 

[transfixer]

The truck only has 59k miles it has a little bigger than stock tire size 265/70-17.

Its still possible it could be timing related, have a shop you trust check it out, see if the timing is changing correctly, other than that I would say check your air filter , a lot of people don't change them as often as they should, myself included.

 

[7 point]

I put a new k&n air filter in it. If it's timing related would my check engine light come on ?

 

[7 point]

I put a new k&n air filter in it. If it's timing related would my check engine light come on ?

 

[model88_308]

The truck only has 59k miles it has a little bigger than stock tire size 265/70-17.

My stock tire was a 265/65(70?)/18. I changed tires and wheels in '09.

 

[7 point]

Sorry 265/65-17 don't know where I got 70 from

 

[transfixer]

I put a new k&n air filter in it. If it's timing related would my check engine light come on ?

Not necessarily, only way to know whats really going on is find a good diagnostic technician and get them to check it out, and by that I mean someone who has the scanners and equipment to check it out,, not just some mechanic who is going to throw parts at it .

 

[7 point]

I will take it to my mechanic that I have used for years

 

[GoldDot40]

A larger diameter tire will turn less revolutions per mile...meaning your speedometer and odometer will be slower. So over the course of 10 actual miles, your odometer may only show 9.7 miles. That will add up over the course of a tank of fuel. On paper, it will certainly appear that you're getting worse mpg...when you "may" not be.

Good idea to have your speedometer recalibrated after you put bigger than stock diameter tires on it.

 

[paulito]

I put a K&N cold air intake on my 2013 F150 and it dropped MPG. About 1.5 cuz I drove it like an idjit. I put larger tires on my 2018 F150 and it also dropped about 1.0 MPG.

I'd say it's not the truck but the changes u made. I like my big tires o. My 2018, but didnt see the benefit of the K&N cold air from the 2013, so didnt add it.

 

[John Cooper]

I remember when I got 17-19 mpg, I get an average of 13-14 now. But I didn't buy a truck for mpg either.

 

[lonewolf247]

A larger diameter tire will turn less revolutions per mile...meaning your speedometer and odometer will be slower. So over the course of 10 actual miles, your odometer may only show 9.7 miles. That will add up over the course of a tank of fuel. On paper, it will certainly appear that you're getting worse mpg...when you "may" not be.

Good idea to have your speedometer recalibrated after you put bigger than stock diameter tires on it.

OP, he's correct on this one. If you went up in tire size, and didn't recalibrate your speedometer, you really are not getting an accurate MPG calculation. Usually, going up in size will hurt your performance, MPG, etc. It's just hard to say exactly how much.

What's the new tire size, vs the stock tire size?

 

[fireman32]

I have an 05 expedition with the 5.4, I only get around 50,000 miles out of my spark plugs. After 50,000 it starts running bad, stuttering between 3-4 gear change and lower gas mileage. New plugs bring it right back to good.

 

[7 point]

That's what I'm thinking .I haven't changed them yet