dysfunction8

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?

Travyforyou

Those trucks are very slow, my friend has a 4.6 and it'll tow decently but it's slow. And ur mileage will get worse if u go to 4.56 gears or even 4.10, it will help pull and give faster off the line speeds but it'll hurt freeway mileage. It is what it is haha I wouldn't do too much to make it faster, trucks are squally slow if its a 4x4. And stock piping I think is 2 1/4" and if u get under 10 mpg u should recalculate or u have a major issue. I have a 2000 4x4 with 33.5" all terrains and I get 14 mpg town and 17 freeway with stock gears and a magna flow and a turndown

greenheadkiller98

Dude it's a truck with a small v8, don't expect a whole lot from all those mods

dysfunction8

I'm not expecting much, but I'm hoping anything will be an improvement. Also, if my highway mileage goes down, I really doubt I'll notice, as I very rarely use the interstate. Most of my long distance driving is on state highways.

jaycarl

I would worry about the MPG more than anything else. Track down why your only getting 10MPG and you will probably find the reason your truck is not performing to your expectations.

Ryanab2

Yea before you start modding it to go faster, you should bring it into a shop and have whatevers broken fixed. Theres clearly something wrong with the engine if its getting 10 mpg. That thing should get like 15 at the lowest

greenheadkiller98

The window sticker on my 2wd ext cab 4.6 with 3.55 gears said 14 city 16 hwy. an that's in 1998 before ethanol.

dysfunction8

ok guys, help me jog my memory on things to look for that may be wrong then. it's been a few years since I've done any troubleshooting on a fuel infected vehicle. my last 2 vehicles have been an '87 Mustang with a 351C swap, and a 1969 F250 with a 360FE....how long are the coil on plugs good for? Have o2 sensors gotten any better, or do they still need replacing every couple years? throttle position sensor? idle air control valve? what else?

greenheadkiller98

I would check plugs, wires, coils, air filter, clean maf, clean throttle body, fuel filter, cats, anything I missed I'm sure someone will chime in

ibd2328

iTrader: (2)

I would make sure you MAF and 02 sensor are good because its a "home cooked" exhaust. You may be running too rich and just wasting fuel.