Recently purchased 2010 F150 lariat with 55,000 miles. 5.4 ltr engine 2wd. I cannot figure out why I am only getting 9 miles to the gallon. The truck runs well, new air filter, engine is clean, I am at a loss. The wheels are slightly larger than specs 265 vs 260. We don't mash the accelerator at traffic lights and most driving is done in town. Not getting any warning lights for anything and there is no smoke coming out of exhaust. I use reg unleaded and sometimes e85. Does anyone have any suggestions? Thanks in advance.

 

Are your tires taller than the stock? If so, your odemeter is not accurate. You are traveling farther than it records. Also, E85 gets about 30% less mpg than E10.

 

Thanks Jim. I used an external gps to see if that may be the problem and the speedometer is accurate and the odometer appeared to be true with the gps. Thanks for the feedback!

 

I would believe 9 mpg on E85.

 

I'll bet you have a bad or lazy O2 sensor causing the PCM to use more fuel, same thing happens when temp sensors report the engine is cold and so the PCM uses more fuel to warm it up.

 

Not quite. Adding fuel to a gasoline engine's combustion cycle helps it run cooler, not hotter. An engine runs somewhat richer when cold because it needs the extra fuel since the fuel doesn't atomize properly at low temperatures and won't ignite reliably.

However, I suppose it's possible an O2 sensor could be malfunctioning without throwing a code.

My old truck (2005 5.4L) would get about 12-12.5 mpg around town using E10 gas on a good day. I know E85 really kills gas mileage, so I agree with glc that if that's the junk you're burning, it may be one cause of the poor performance. The larger tires are also a big detriment. They reduce the effective force you can apply to the road to get moving and so make the engine work harder.

If your GPS reports your speed is about 3% lower than your speedometer, then your odometer is accurate. The speedometer in F150's reads about 3% high due to errors in converting digital data from the PCM to an analog readout. If the GPS speed is the same as the dashboard speed, the PCM thinks your distance driven is shorter than actual. To determine if your odometer is accurate in a comparison with the GPS, you need to drive a significant distance, like about 100 miles.

- Jack

 

OR heavier than stock? These trucks seem to be sensitive to tire weight! Has the engine been "tuned" or had other "mods' done on it?

My STOCK 2010 5.4 FX-4 gets about 14 MPG in town and about 19 on the highway and I have a heavy foot.

 

You are correct on the weight. On my 2011 when I replaced the OEM tires with the same size Toyos, they had a slightly wider profile and weighed 9 lbs more each. That translated to about 1.2 loss in mpg.

 

I appreciate the help. I will consider just about anything to get it over 11 or 12. Have not had it tuned up, and that appears to be my next step. Was hoping I wouldn't have to take it in, but that may be the only way to determine the issue. Thanks again to all for your feedback.

 

In town driving and E85 are probably your two main culprits.

 

No, I think there's more going on. I buy the cheapest gas around (E-85) and do a lot of in town driving but my mileage isn't that bad.

OP how far apart are traffic lights or stop signs were you drive? Stopping at lights and then having to accelerate back to speed KILLS my MPG! If I reset my MPG meter after I'm already up to speed (45-ish) and drive for mile my MPG will 22 to 25 MPG. If I stop at a light, wait a minute and then accelerate back to 45 MPH (at a normal rate). My MPG will drop to something like 11. Drive another mile and repeat and it will drop to 8!

If I had to stop every 1/4 mile or so or if I floored it getting away from a stop then I hate to think how bad my MPG would be! Fortunately I'm not too far from a couple of toll roads and if I go very far I take them. Once I get on those, my MPG goes back up. OTOH I do have to pay tolls but that's outside of this discussion.

 

I had a 2010 that I got rid of 3 years ago. I drove it 106,000 miles in 2.5 years. It was a 4wd and it never got near that poor of mileage. I got 16 on the interstate and 17.5 on two lane roads running 60 to 65. So there is something way wrong here.
The tires shouldn't be that big of deal. Besides, the number you gave is the cross section width in mm and doesn't translate to height completely. The second number of the tire size is called aspect ratio and does tell you the height of a tire. Either way, that is not the issue here
I would look at a thermostat that is stuck open or a sensor that is malfunctioning and tricking the computer into running to rich. It could be a combination of two issues. It could be a plugged converter. Or an 02 sensor that is reading incorrectly. Clearly this engine is not metering fuel correctly. Good luck and let us know how it goes. Chasing these things can be head scratchers.

 

From everything you've posted, your truck is not running rich. I personally think your odometer is lying to you, due to the larger tires. So, it shows a shorter distance than you've actually driven. The larger tires put the engine under a greater load too, forcing your foot down on the gas pedal to keep the whole mess moving. Add E85, and you lose even more mileage.

As I said, to verify the odometer, you need to drive a significant distance, like 100 miles. Anything less and your readout doesn't have sufficient granularity.

- Jack

 

What size tires do you have? The factory tires for that truck are either a 265/60R18 or 275/55R20. So it sounds like your tire size is pretty close unless your aspect ratio (second number) is 75 or something like that. Then they would be to tall.
Try not running any e-85 and see if that helps. It still acts like something else is going on.

 

OP,

Go read post #20 and watch the videos and then do the test. This could easily be the source of your problem! Report back on on what you find. Good or bad.

https://www.f150online.com/forums/20...ml#post5158761