New truck, few questions - Ford F150 Forum

lobuzz311 · 05-26-2009, 04:33 PM

Hi All,

I just got a 2004 F150 Lariat and absolutely love the thing. I got it to tow a boat, and it does that beautifully. I do have some questions, though.

The truck has the 5.4 engine, is lifted 4" with 18" wheels & 35" tires. What should the gas mileage for the truck be? Like I said, I am doing some towing with it (a 20' ski boat) & driving it around town. I have not really taken it on the freeway since getting it. The trip computer is giving me an overall average mileage of 8.6 mpg. I know that this is a heavy vehicle, but even with the big tires and towing (5 miles to the lake each way, maybe), I feel like it should be at least closer to the 14/18 advertised.

Any thoughts?
Thanks!

MHC-F150 · 05-26-2009, 05:19 PM

Couple items of thought. Did the prior owner recalibrate the speedo after installing the larger tires? Did the prior owner re-gear the truck (from 3.55 or 3.73 to 4.10 or 4.56)? What are your driving habits (heavy on the gas)?

lobuzz311 · 05-26-2009, 06:06 PM

Quote:

Originally Posted by MHC-F150

Couple items of thought. Did the prior owner recalibrate the speedo after installing the larger tires? Did the prior owner re-gear the truck (from 3.55 or 3.73 to 4.10 or 4.56)? What are your driving habits (heavy on the gas)?

Thanks for the reply.

Here's what I know:
The speedo has not been recalibrated, as far as I can tell. I tested it against my Garmin GPS, and it's off by about 5mph.
I am also not sure about the gearing having been changed. I purchased the truck at a Ford dealership, and I asked if the truck had been re-geared to compensate for the big tires. The salesman said that it had, as part of their "safety" inspection/fixes. I don't know if he was just shooting smoke up my ass, or if that's actually the case. Is there a way to tell how it's geared without opening things up?
My driving habits are pretty mellow. I am quite content lumbering around pretty slowly, as I have other much smaller cars I can use for spirited driving.

PawPaw · 05-26-2009, 09:02 PM

You may want to go with a programmer such as an Edge to adjust the speedometer error. My truck is leveled with 35" tires and I get a consistant 16-18mpg on the highway. Look's like the same truck except for the paint and a little more lift. I couldn't live with 8 mpg since I drive close to a hundred miles a day round trip to work.

boilerup15 · 05-26-2009, 09:45 PM

Just curious, do you know what kind of lift you have on your truck?

lobuzz311 · 05-26-2009, 11:26 PM

Quote:

Originally Posted by PawPaw

You may want to go with a programmer such as an Edge to adjust the speedometer error. My truck is leveled with 35" tires and I get a consistant 16-18mpg on the highway. Look's like the same truck except for the paint and a little more lift. I couldn't live with 8 mpg since I drive close to a hundred miles a day round trip to work.

Thanks for the tip. I will look into that. Since the speedometer isn't calibrated, the mpg on the trip computer will be off as well, of course.

Quote:

Originally Posted by boilerup15

Just curious, do you know what kind of lift you have on your truck?

I don't know what the lift kit is... why?

boilerup15 · 05-27-2009, 12:13 AM

I am wanting a lift but not 6" I think the 4" would be perfect.

MHC-F150 · 05-27-2009, 10:36 AM

Quote:

Originally Posted by lobuzz311

Thanks for the reply.

Here's what I know:
The speedo has not been recalibrated, as far as I can tell. I tested it against my Garmin GPS, and it's off by about 5mph.
I am also not sure about the gearing having been changed. I purchased the truck at a Ford dealership, and I asked if the truck had been re-geared to compensate for the big tires. The salesman said that it had, as part of their "safety" inspection/fixes. I don't know if he was just shooting smoke up my ass, or if that's actually the case. Is there a way to tell how it's geared without opening things up?
My driving habits are pretty mellow. I am quite content lumbering around pretty slowly, as I have other much smaller cars I can use for spirited driving.

Like others stated, either get a programmer or take it into Ford to recalibrate the speedo. Couldn't tell you what Ford would charge for such service. But a programmer would be your best bet and bang for your buck.

Check what the original gears were first, should be on your door jam under the "Axle Code". The link below will give you a chart to determine the coding of your stock gears. If it's two numbers (36, 39, etc) you know the stock gears were not Limited Slip. Most likely though since you have the Lariat, it came with LS, which would be coded by one letter followed by one number (B9, B6, etc). Your truck more than likely came with 3.73LS, but may have come with 3.55LS. Any code ending in 9 is a 3.55, ending in 6 is 3.73, ending in 5 is 4.10. Maybe your problem is you have stock 3.55 gears which are struggling to get them tires moving.

http://www.ford-trucks.com/article/i...de_Chart_.html

Without opening up the rear end it's hard to tell. Either check to see if there is any noticable markings or fluid drip spots that may indicate it's been opened up before. Otherwise, and not likely, check to see if the prior owner put a sticker on the rear diff, in the door jam, under the hood or in the owners manual.

Thunderslide · 05-27-2009, 01:50 PM

it is not all that hard to figure out the gear ratio. all you need to do it rotate the tire one turn and count the turns on the drive shaft. for example assuming all one tire rev. drive shaft about 3-1/2 rev 3.55, 3-3/4 rev 3.75, little more than 4 revs 4.10, and 4-1/2 revs, you guessed it 4.56 because it is a ratio it is 4.56:1 thus 4.56 turns in (drive shaft), 1 turn out (wheel).

lobuzz311 · 05-27-2009, 02:09 PM

Quote:

Originally Posted by MHC-F150

Like others stated, either get a programmer or take it into Ford to recalibrate the speedo. Couldn't tell you what Ford would charge for such service. But a programmer would be your best bet and bang for your buck.

Check what the original gears were first, should be on your door jam under the "Axle Code". The link below will give you a chart to determine the coding of your stock gears. If it's two numbers (36, 39, etc) you know the stock gears were not Limited Slip. Most likely though since you have the Lariat, it came with LS, which would be coded by one letter followed by one number (B9, B6, etc). Your truck more than likely came with 3.73LS, but may have come with 3.55LS. Any code ending in 9 is a 3.55, ending in 6 is 3.73, ending in 5 is 4.10. Maybe your problem is you have stock 3.55 gears which are struggling to get them tires moving.

http://www.ford-trucks.com/article/i...de_Chart_.html

Without opening up the rear end it's hard to tell. Either check to see if there is any noticable markings or fluid drip spots that may indicate it's been opened up before. Otherwise, and not likely, check to see if the prior owner put a sticker on the rear diff, in the door jam, under the hood or in the owners manual.

I looked up the axle code, and it was B6. So it looks that it came stock with the 3.73LS gearing.

Quote:

Originally Posted by Thunderslide

it is not all that hard to figure out the gear ratio. all you need to do it rotate the tire one turn and count the turns on the drive shaft. for example assuming all one tire rev. drive shaft about 3-1/2 rev 3.55, 3-3/4 rev 3.75, little more than 4 revs 4.10, and 4-1/2 revs, you guessed it 4.56 because it is a ratio it is 4.56:1 thus 4.56 turns in (drive shaft), 1 turn out (wheel).

That's a great idea. Now my only problem will be trying to figure out how to jack up the truck... the jack that came with it is going to be quite insufficient.