Hello all, I just recently bought an '03 F150 4x4. It's got a 4.6 with an auto trans. This thing is a turd! I am coming from an '87 mustang, so that may have something to do with it, but it's pretty slow, and it currently gets less than 10mpg. So far from what I can tell, it's only had a couple of modifications (K&N intake, home cooked exhaust, and larger tires[285/75R16]), so naturally I feel the need to go in and make it my own, and at least get it to accelerate decently. Here's what I have on my list to do.

re-gear the truck (4.10's or 4.56's)
purchase a tuner
shorty headers
fix the home cooked exhaust (more on it in a second)
perhaps some underdrive pulleys and an electric fan

That should about do it. The exhaust is an issue with me. The P/O had the Y pipe cut out, and ran duels back to the axle and dumped them, which is fine, but the piping that was used was only 2 1/4", and it was crush bent, so you're talking right around 2" in the bends....factory was at least 2 1/2", correct? The thing sounds good, but I can't imagine the smaller piping is helping it (maybe not hurting, but definitely not helping). Does anyone have any other suggestions on potential mods to help the truck out?

 

I like the mods you have listed. The truck sounds like it needs some TLC. I had a 97 F-150 with the 4.6 and it was fun to drive. I did chip it and did cat-back dual exhaust. I also changed all the fluids to synthetics, as well as changed the transmission filter. BTW, I think I got close to 13 MPG, even when pulling a loaded 10' enclosed cargo trailer and cruise set at 85.

 

I'd be more than happy with 13mpg....I understand it's a truck, and I didn't buy it for the mileage, but if it's not getting at a minimum what it's supposed to, then something is definitely wrong

 

All new fluids and a tune will go far.

I forgot...I also did a coil pack, plug, and wire upgrade. I got a kit from Troyer Performance.

 

Sounds like something else might be wrong. Have you checked for any CEL codes. I have a 97 f150 4x4 supercab, auto tranny with the 4.6 and I average 17 mpg driving around town. And I have checked it more than once. Right now mine is stock 3.55 gearing and 245/75/R17 tires. I talked to a friend with a all stock truck but with 35/12.50.R17 tires and he averages 15.

I know future plans for me is 35's, under drive pulleys, programmer, and E-fans. after that if my power sucks I plan on 4.10 gears.

 

Get ready for flame, but having owned 1 97 5.4, two 98's (one 4.6 one 5.4) and a 99 4.6 I can tell you the 4R70W trans behind the 4.6 is junk and not built for this truck. I blew both of mine at low miles (under 100k) and the 4.6 is an underpowered turd in these trucks as you said.

My E4OD 5.4L trucks were and are MUCH better. Power is great, low end is great and both trannies went over 200k miles, my 97 went to 230k and my current 98 has 215k and still kickin. My old 98 4.6 (bought it new in 98) went to 80k and POP goes the tranny. My current 99 went to 85k miles and POP goes the tranny. So point is take is easy on the trans and power you feel may be normal. I get 14-15 mpg with my 5.4 trucks and 13-14 mpg with my 4.6 trucks. 10 is way out of line unless you're putting the peddle through the floor all the time, so you may want to look into a possible issue.

 

Sounds like you just got unlucky. Personally I think the 4R70W is a decent trans, defaintly better than the E4OD. Never had much luck with those. The only problem with the 4R70W is it is too sluggish. It's a very smooth trans, but that smoothness affects performance. The J mod fixes that though. I always wanted to do it, but never got around to it.

That being said, the E4OD I think can handle more power and is mainly based off the C6, which IMO was the best auto trans Ford ever made.

Here's some interesting info on Ford auto trannys http://www.baumannengineering.com/alphabet.htm

 

Other things being equal, has anyone else ever consistently gotten better MPG on 5.4 than 4.6?

My understanding was that, all things being equal, the 4.6 returned as much as 2-3 MPG more than the 5.4, often over 50 extra miles out of each tankful.

 

What is the J mod??? I have a 4R70W in my truck now 150,000 miles and no problems.

 

I must weigh in on this subject by referring back to the original post.
First thing is the poster is coming from a hot rod point of view trying to compare a 6500 plus lb truck to an 87 Mustang weighing in the area of 32 to 3400 lbs with a 5L motor.
Not going to happen! There is no comparison.
Next the idea of shorty headers is foolish on a truck application.
It will not get you anything but lose some low end.
If you run around at 4000 rpm and higher maybe you will see a difference.
Most don't run that way.
The motor is 261 cu in to boot.
The cams in these motors don't start to come on until over 2200 rpm and begin to pull hard at 3000 to about 4500 then your done.
99% of the time we all are running below 2000 in OD at the average legal speeds. The torque is quite low below 2000 rpm.
The transmissions are fine as they are but could use a bit firmer upshifts than the factory provides.
The 4R70W has been around a long long time. The W means a low ratio first gear. That can be changed if you want to make the investment in normal gear ratio spreads to go along with a 4:11 or 4:56 rear gears.
With your stated poor fuel mileage; what mods have been done? If there are any, maybe they are the cause.
You need to get a Scanner and look at the live data for an issue you could not do with the Mustang.
Bottom line is you need to update your perspective between the two vehichles and years.
These trucks do not respond the same way your Mustang did to outside changes.
You will spend a lot of money trying before you find this out.
The best performance per dollar spent to get back a worthwhile increase is rear gears, a higher stall speed converter and a tuner to optimize the changes.
Forget the cold air intakes and aftermarket filters etc.
There are few cats that would offer any performance increases.
Good luck.

 

the 4.6 is a dog. i own one. that being said it runs well and it works for me. my truck is used daily and i pull campers and boats. the stall speed on the 4r70w seems to increase with temp though but whos cares it still works. engagement speed maybe? my terminology is wrong but the truck when hot does not go until about 2200 rpm's compared to about 1800 when cold. the numbers are estimated. again though no big deal for me.

 

Really? An '03 F150 4X4 is "a 6500 plus lb truck? Had thought they were well under 5000 lb?

When "referring back to the original post" the Gorilla In The Room has to be "it currently gets less than 10mpg"! The "home cooked exhaust....285/75R16" tires & other comments raise doubts about owner's math. However, he does seem to grasp that "something is definitely wrong"?

Quite likely that if it was put right it wouldn't be a "gutless wonder".